Methods for controlling catalytic processes, including the deposition of carbon based particles

Methods and apparatus for controlling a catalytic layer deposition process are provided. A feed stream comprising a carbon source is provided to a catalyst layer. An asymmetrical alternating current is applied to the catalyst layer. A polarization impedance of the catalyst layer is monitored. The polarization impedance can be controlled by varying the asymmetrical alternating current. The controlling of the polarization impedance provides control over the structure and amount of carbon particles deposited on the catalyst layer. The carbon particles may be in the form of nanotubes, fullerenes, and/or nanoparticles.

BACKGROUND OF THE INVENTION

The present invention relates generally to catalytic processes. More particularly, the present invention provides methods and apparatus for controlling a catalytic layer deposition process, including the deposition of carbon based materials in the form of nanotubes or fullerenes.

Catalyst systems are employed extensively to reform light hydrocarbon streams, i.e. reduce methane and other light hydrocarbons to hydrogen, and to remediate exhaust streams, including reducing and/or oxidizing internal combustion engine exhaust to innocuous compounds.

A problem encountered with prior art catalyst systems is poisoning of the catalyst. One source of such poisoning is the adsorption/infiltration of oxygen-containing species such as carbon monoxide. Carbon monoxide interferes with the catalysis mechanism. Another source of poisoning is the deposition of carbon.

Methods of addressing catalyst poisoning include applying to the catalyst a direct current (DC) electric field and/or heating it to an elevated temperature, i.e. about 300° C. to about 800° C. Most commonly, an electric field and heat are concurrently applied. Application of a DC electric field and heat expels or pumps oxygen-containing molecular species from the catalyst. Examples of the prior art application of DC current and/or heat to a catalyst are described in the following: U.S. patent/application Nos. 2001/0000889; 2002/0045076; 4,318,708; 5,006,425; 5,232,882; 6,214,195; and 6,267,864.

For example, it is known that the yield of the catalytic processes can be increased (enhanced) by the polarization of the catalytic interfaces under certain conditions. The overall voltages applied are low (up to 1-2 V), but they are applied across interfaces which are very thin (e.g., the thickness of the interface is on the order of magnitude of ˜1 nanometer, which is close to the diameter of a small molecule). This leads to the creation of very high electric fields across the polarized interfaces: the order of magnitude of these fields can be as high as 106V/cm or more. Such high fields polarize (excite) the molecules of the substances that react in the catalytic system, and can pump ions across the interface. The result of these processes is that under controlled conditions, the concentration and the activity of catalytic sites available for the reaction increases beyond the concentration that was determined by the preparation process of the catalyst. This process is known in the prior art as the NEMCA (Nonfaradaic Electrochemical Modification of Catalytic Activity) effect. However, the enhancement of the catalytic activity achieved by the NEMCA effect is very difficult to control.

One problem encountered with application of a DC electric field to catalyst systems is a lack of a means for monitoring and sensing the level of poisoning present in the catalyst in real time or on a continuous basis. This lack of means to monitor and sense the level of poisoning in the catalyst in real time hinders precise and timely application of the DC electric fields. Precise and timely application of DC electric field is important because if the field is too weak, the rate of expulsion of oxygen-containing species may be too low and such species may accumulate. If the DC field is too strong, the incidence of catalytically effective sites in the catalyst may be reduced.

The application of heat to catalyst systems also has the problem of a lack of real time control means, and also suffers from imprecise effects of temperature on catalyst behavior and the physical structure of the catalyst system. If the temperature of the catalyst is too low, the catalyst may become fouled (dirty) and the kinetics of the catalyzed reaction may be negatively altered. If the temperature is too high, the kinetics of the catalyzed reaction may be negatively altered and/or the microstructure of the catalyst may be destroyed.

Nanotubes are used in an ever increasing number of commercial applications (e.g., composite materials, catalysts, structural materials for medical use, structural materials in the defense and avionics industries, electronic devices, electrochemical devices (e.g., battery electrodes and sensors), hydrogen storage, and the like). It is also well-known to produce carbon nanotubes and/or fullerenes in bulk using various methods, such as electrochemical techniques (as disclosed for example in Zhou, et al, “Synthesis of Carbon Nanotubes By Electrochemical Deposition at Room Temperature” Carbon 44 (2006) 1013-1024), arc evaporation, sputtering, Chemical Vapor Deposition (CVD) and Plasma Enhanced Chemical Vapor Deposition (PECVD). The yields achieved with these methods are fairly low, hence the price of materials with well-defined characteristics can be very high, reaching more than $20,000/gram for some types. To the best of applicant's knowledge, to date there has not been a control process which enables a high yield at low cost while at the same time providing control over the characteristics and structure of the carbon nanotubes.

It would be advantageous to provide an active catalytic process, including an active catalytic layer deposition process, as opposed to the passive nature of prior art catalytic processes.

It would be further advantageous to provide a simple, real time way to control the enhancement of catalytic reactions and the deposition of a fullerene/nanotube layer.

It would be still further advantageous not only to enhance the oxidation reactions in the catalyst, but also to oxidize carbon particles (soot) to CO and subsequently to CO2, resulting in a drastic decrease (and possibly complete elimination) of soot particles from the diesel exhaust gases and also to regenerate the catalyst.

It would also be advantageous to control the catalytic reaction in order to control the characteristics of a layer deposited on the catalyst. In particular, it would be advantageous to control the catalytic reaction so that carbon-based materials are deposited on the catalyst layer in the form of carbon nanotubes and/or fullerenes, and to enable removal of the carbon nanotubes/fullerenes for use in a wide variety of commercial applications.

The methods, apparatus, and systems of the present invention provide the foregoing and other advantages.

SUMMARY OF THE INVENTION

The present invention provides methods and apparatus for controlling a catalytic layer deposition process, including the deposition of carbon based materials in the form of nanotubes, fullerenes, and/or nanoparticles.

In one example embodiment of the present invention, a method for controlling a catalytic layer deposition process is provided. The method comprises providing a feed stream comprising a carbon source to a catalyst layer, providing an asymmetrical alternating current to the catalyst layer, monitoring a polarization impedance of the catalyst layer, and controlling the polarization impedance by varying the asymmetrical alternating current. The controlling of the polarization impedance provides control over the structure and amount of carbon particles deposited on the catalyst layer.

The controlling of the polarization impedance may further comprise correlating a time variation of the polarization with at least one of a thickness and the structure of the deposited carbon particles on the catalyst layer. Measured polarization impedance values from the monitoring may be correlated to a database linking each of the polarization impedance values with data regarding at least one of the chemical nature, structure and average value for ratios of deposit volume/unit of surface area.

In a further example embodiment, the method may further comprise applying a carrier gas containing oxygen to the catalyst layer, monitoring a partial pressure of oxygen in the carrier gas at the catalyst layer, and adjusting the polarization impedance based on the monitoring of the partial pressure of oxygen in order to enhance the deposition of the carbon particles on the catalyst layer.

The catalyst layer may be supported on or in close contact with a solid electrolyte. An ionic conductivity of the solid electrolyte may be within a range of between approximately 1 to 10−4ohm−1*cm−1. The catalyst layer may comprise one of platinum, a semiconducting oxide, a semiconducting materials, or the like. The solid electrolyte may comprise one of stabilized zirconia, stabilized bismuth oxide, forms of beta alumina, Nafion, a mixed conductor, or the like.

The carbon deposits may comprise at least one of nanotubes, fullerenes, and nanoparticles. The method may further comprise harvesting the at least one of nanotubes, fullerenes, and nanoparticles from the deposited carbon particles.

At least one of an amplitude and a phase of the asymmetrical alternating current may be varied in order to regenerate the catalyst layer subsequent to the harvesting.

The carbon source may comprise at least one of CO, CO2, hydrocarbons, oxygenated hydrocarbon-derivatives, organic compounds, and the like. The feed stream may comprise one of water or steam.

The method may also include one of extracting or electrically pumping oxygen from the catalyst layer to generate a reduction reaction for initiating or enhancing the deposition of the carbon particles onto the catalyst layer.

The deposition of the carbon particles on the catalyst layer may be monitored. Monitoring of the deposition of the carbon particles may comprise monitoring a rate or structure of the carbon particles deposited on the catalyst layer. Alternatively, the monitoring of the deposition of the carbon particles may comprise monitoring at least one parameter which describes an interfacial impedance of the catalyst layer, and determining an amount of the carbon particles deposited on the catalyst layer as a function of values of the at least one monitored parameter. The at least one monitored parameter may comprise at least one of the monitored polarization impedance and a phase angle of the interfacial impedance.

The method may further comprise varying at least one of an amplitude and a phase of the asymmetrical alternating current in order to control characteristics of the deposited layer. The at least one of the amplitude and the phase of the asymmetrical alternating current may be varied to bring the polarization impedance to a value within a predetermined range of values when the polarization impedance value falls outside of the predetermined range. The predetermined range may be a range of values around an original polarization impedance value of the catalyst layer prior to use. At least one of the amplitude and the phase of the asymmetrical alternating current may be varied to achieve a phase angle of an interfacial impedance of the catalyst layer which is within a range of between approximately −10 degrees and +10 degrees.

In a further example embodiment, at least one of water, steam, oxygen, and heat may be applied to the catalyst layer. The application of the at least one of the water, steam, oxygen, and heat may be controlled in order to control the deposition of the carbon particles on the catalyst layer.

A carrier gas containing oxygen may be applied to the catalyst layer. The partial pressure of oxygen in the carrier gas may be controlled in order to enhance the deposition of the carbon particles on the catalyst layer.

In one example embodiment, the feed stream may comprise at least one of a liquid phase and a gas phase. The method may further comprise at least one of (a) varying at least one of a phase and an amplitude of the alternating current, and (b) controlling at least one of an amount of water, steam, and oxygen applied to the catalyst layer or to a deposited layer formed by the deposition of the carbon particles in order to provide at least one of (i) a reduction of the at least one of the liquid phase and gas phase in contact with the catalyst layer, and (ii) stimulate growth of the deposited layer. Further, an amount of heat applied to the catalyst layer may be controlled in order to further control at least one of the structure and a thickness of the deposited carbon particles on the catalyst layer.

The present invention includes a further method for controlling a catalytic layer deposition process. The method comprises providing a feed stream to a catalyst layer, the feed stream comprising at least one of carbon, silicon, doped silicon, silicon carbide, gallium arsenide, niobium, and boron (or the like). An asymmetrical alternating current is applied to the catalyst layer and a polarization impedance of the catalyst layer is monitored. The polarization impedance may be controlled by varying the asymmetrical alternating current. A deposition layer is formed on the catalyst layer as a function of the controlling of the polarization impedance. The deposition layer may comprise at least one of nanotubes, fullerenes, and nanoparticles.

The present invention also includes apparatus for controlling a catalytic layer deposition process corresponding to the above-described methods. For example, the present invention includes an apparatus for controlling a catalytic layer deposition process which comprises means for providing a feed stream comprising a carbon source to a catalyst layer, means for providing an asymmetrical alternating current to the catalyst layer, means for monitoring a polarization impedance of the catalyst layer, and means for controlling the polarization impedance by varying the asymmetrical alternating current. The controlling of the polarization impedance provides control over the structure and amount of carbon particles deposited on the catalyst layer.

The apparatus may include additional features of the methods described above.

DETAILED DESCRIPTION

The ensuing detailed description provides exemplary embodiments only, and is not intended to limit the scope, applicability, or configuration of the invention. Rather, the ensuing detailed description of the exemplary embodiments will provide those skilled in the art with an enabling description for implementing an embodiment of the invention. It should be understood that various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the invention as set forth in the appended claims.

Example embodiments of the present invention have been found to enhance the catalytic activity of prior art systems by a factor of 2 (and possibly more) as a consequence of the action of a process called the DECAN process (Dynamic Enhancement of the Catalytic Activity at Nanoscale), developed by Catelectric Corp., the assignee of the present invention.

Whereas the prior art NEMCA effect is essentially a DC phenomenon, the DECAN technology developed by Catelectric is built upon processes that occur under an alternating or variable current/voltage scheme.

The DECAN process provides a simple, real time way to control the enhancement of catalytic reactions. The DECAN process is described in detail in Applicant's commonly-owned U.S. Pat. No. 7,325,392, which is incorporated herein and made a part hereof by reference.

The real time control of the enhancement process in accordance with the example embodiments of the present invention is essential for the efficient operation of an enhanced catalytic system. With Applicants' DECAN process, measurements sensed from the catalysts are fed into a simple electronic control module, which adjusts, also in real time, the polarization state of the interface through the application of alternating or variable voltages and currents.

Seetharaman et al., in an article entitled “Transient and Permanent Effects of Direct Current on Oxygen Transfer Across YSZ-Electrode Interfaces” [Journal of the Electrochemical Society, Vol. 144, no. 7, July 1997] (“Seetharaman”), identified and described a hysteresis effect at the three-phase boundaries in Pt/YSZ/gas environments, when the interface transitions from a cathodic to an anodic current (see, e.g., FIG. 8 of Seetharaman). The concentration of the oxygen-containing sites present at equilibrium can be modified by the passage of a cathodic or an anodic current, respectively. These changes have a dynamic effect on the properties of the interface, as, for instance, on its catalytic properties. The present invention achieves control of this hysteresis effect through the real-time monitoring of certain electrical properties of the catalytic interface. These electrical properties are determined as an average value over the whole interface involved in the catalytic process, and are therefore reflecting in real time the average catalytic activity.

Seetharaman et al. assigned this hysteresis effect to the coexistence of different species, including species pumped electrochemically to or away from the interface. Subsequent work [see, e.g., Seetharaman et al., “Thermodynamic Stability and Interfacial Impedance of Solid-Electrolyte Cells with Noble-Metal Electrodes [Journal of Electroceramics, 3:3, 279-299, 1999], has shown that this hysteresis is related to the transient formation of partially blocking species at the charge transfer interface (the three phase boundary (TPB)) as illustrated inFIGS. 1 and 2.

These species (e.g., oxygen-containing species (OCS)), are active in the charge transfer and in the electrocatalytic reactions occurring at the TPB. When OCS is present at the TPB, it may block the reaction if it is insulating with respect to ions as well as electrons (seeFIG. 2a). Electrically, the interface may be represented by a capacitor. On the other hand, the OCS may only be partially blocking. The OCS may then act as an intermediate step in the charge-transfer process (seeFIG. 2b). Such a result is likely if the OCS consists of oxygen loosely bonded to the metal surface. In this case, the interfacial process is associated electrically with an impedance ZOCS(referred to herein as “interfacial impedance”).

The magnitude of the interfacial impedance, ZOCSdepends on the strength of the Metal-O bonds that need to be broken or established in the oxygen-transfer process.

Therefore, the value of the interfacial impedance is directly related to the concentration of the OCS, which, in turn, is related to the concentration of the electrocatalytic sites at the interface. Accordingly, the values of the interfacial impedance for a given system are therefore reliable indicators of the concentration of catalytic sites, which determines the rate of the reaction occurring at the interface.

The correlation between the interfacial impedance and the yield of the catalytic reaction is a complex function, which may be determined experimentally. In accordance with various embodiments of the present invention, the yield of the system can be maximized by a continuous control of the NEMCA parameters by the alternating current applied to the system (the pattern of change of the voltage and current density in the time domain) and by monitoring the complex (AC) impedance of the interface. This is the principle of the DECAN process of the present invention.

Various example embodiments of the present invention provide the capability to force, enhance, and/or boost the reduction of NOx(effectively controlling the pumping of the oxygen out of the NOxmolecular species) beyond the capability of the current state-of-the-art catalytic systems. The pumping of oxygen away from the interface provides also the reductive conditions necessary to nanotubes/fullerene deposition.

Certain embodiments of the present invention also provide the capability to force, enhance, and/or boost the oxidation of CO to CO2. As a corollary to the enhancement of the oxidation reactions, example embodiments of present invention provide the ability to oxidize carbon particles (soot) to CO and subsequently to CO2, resulting in a drastic decrease (and possibly complete elimination) of soot particles from the Diesel exhaust gases. However, it has not yet been determined what will happen with the other, minor components of the exhaust gases (inorganic ash), which is not the focus of the present invention. However, those skilled in the art will appreciate that the addition of an electrostatic filter downstream from the catalytic converter may provide one solution for dealing with these components. Such filters may be similar in design to those used in cement production.

Additionally, example embodiments of the present invention also enable regeneration of the catalyst in-situ, with a slight hysteresis.

Further, example embodiments of the present invention provide a built-in sensing capacity for sensing the changes in the gas composition based on the quantification of the trends in the subsets of a matrix of data providing the correlation between initial (pre-DECAN) gas composition at a given temperature, and the parameters of the DECAN process (real and imaginary components of the impedance, pattern of the application of variable voltage, pattern of the application of variable current, the pattern of the cross-correlation of the voltage and current (expressed by the matrix characterizing the vectorial product of the current and voltage, which are complex quantities in the time domain). A Fast Fourier Transform FFT algorithm may be used to generate a synthetic characteristic based on the response of the gas composition to the applied voltage/current, i.e., as a fingerprint of a change in composition.

Polarization impedance is the difference between impedance measured at low and high frequencies of alternating current. Polarization impedance can be calculated according to the following formulas I and II:
icorr=[βaβc/2.303(βa+βc)][1/Rp]  (I)
Rp=|Z(jw)|w→0−|Z(jw)|w→∞(II)
wherein icorrequals a steady state corrosion current;
βais the Tafel constant for an anodic reaction;
βcis the Tafel constant for a cathodic reaction;
Rpis the polarization impedance (ohm);
w=2×π×f wherein f is the frequency of the alternative current applied and expressed in hertz (Hz);
j is the imaginary unit number (−1)1/2;
Z(jw) is the complex impedance of the interface as a function of the frequency (ohm);
(jw)|w→0is the complex impedance of the interface when the frequency approaches zero (ohm); and
(jw)|w→∞is the complex impedance of the interface when the frequency approaches a very high frequency (ohm).

Test frequencies will vary depending on the characteristics and requirements of the system, but suitable low frequencies typically range from about 0.1 Hz to about 100 Hz and suitable high frequencies typically range from about 10 kilohertz to about 5 megahertz. Polarization impedance is typically expressed in ohm. The method for calculating polarization impedance is set forth inApplications of Impedance Spectroscopy, J. Ross McDonald, p. 262, John Wiley & Sons (1987), which is incorporated herein by reference.

In the present control system, the polarization impedance generally corresponds to the difference or drop in AC current across a catalyst layer/electroconductive support, which will vary in structure depending upon the structure of the catalyst system. The difference in AC current will usually be between the first electrode/second electrode and the AC sensor. The polarization impedance is obtained when the impedance is measure at a low and a high frequency.

An example embodiment of a control system for controlling the DECAN process in accordance with the present invention is shown inFIG. 3and is generally referenced by the numeral10. Control system10has an electroconductive support12and a catalyst layer14situated thereon. A current control unit28communicates with and controls and provides DC current to a first electrode17and a second electrode18through current cables20. First electrode17is contiguous to and in electrical contact with electroconductive support12. Second electrode18is contiguous to and in electrical contact with catalyst layer14. Current control unit28also controls and provides AC current to first electrode17and second electrode18through current cables22. A polarization impedance measurement unit26communicates with AC sensors16, which are contiguous to and electrical contact with catalyst layer14through data transmission cables24. Control system10also has a heater36and a heating control unit34. Heating control unit34communicates with heater36through an interface30and a data transmission cable24. The current control unit28, polarization impedance measurement unit26, and heating control unit34communicates with and are controlled by a central processing unit32through interface30. When control system10is in operation, the process throughput such as a hydrocarbon stream or combustion exhaust will contact catalyst layer14as it impinges or otherwise traverses it. Electrodes may take any electroconductive form, but usually take the form of an electrically conductive wire or conduit contacting catalyst layer14or support12.

FIG. 4shows an alternate embodiment of a structure for implementing the DECAN process in accordance with the present invention. It should be noted that while certain of the layers54,56, and58shown inFIG. 4are required to reduce to practice the DECAN process in accordance with the present invention, not all of them are necessary. For example, at least two of these layers must be present. The remaining layer may be present or not, depending on the application of the invention or desired results.

FIG. 4shows an electronic control device50capable of sending low amplitude AC signals (in the frequency range 1 Hz to 500 kHz), and, simultaneously, DC signals (at voltages between +2 V and −2 V), as well as low frequency (below 1 Hz), variable current and voltage. The operation of this electronic control device may be controlled by an externally programmable control unit52. The details of the software governing the operation of this programmable control unit are not the focus of the present invention.

An underlying electronic conductor54may be provided having an electrically contiguous/continuous phase. This material can be deposited on a sustaining insulating substrate, one example of which is cordierite. Other existing materials, or materials to be developed, having these properties may also be used with the present invention. Alternatively, this material can be a metallic member (a corrugated structure, a stack of sieves or any other structure with open, percolating channels, tortuous or not).

An electrically contiguous/continuous layer56of an ionic conductor (which may be any cationic or anionic material; such as Nafion-like materials, stabilized zirconia, and others as is known in the art) may also be provided. This layer56can be deposited by washcoat-like techniques, by CVD, by plasma-spraying, by electrophoresis, and or any other suitable process leading to a thin film of catalyst deposited on the conducting or semi-conducting substrate54.

An electrically contiguous/continuous layer58of an electronic or ionic conductor (different from that of the previous layer54or56) may also be provided. The ionic conductor of layer58may be any cation or anion-conducting material; such as Nafion-like materials, stabilized zirconia, and others as is known in the art). The electronic conductor can be a carbide, a doped oxide, doped silicon or any other conducting or semiconducting material, single-phase or mixed-phase. This layer58may be deposited on top of the previous layer (either layer54or56) by any of the techniques discussed above. The catalyst, as fine particles, is included in this layer58, which comes in contact with the phase carrying the substance(s) whose reaction is to be catalyzed. Alternately, the catalyst can be deposited on the surface of this layer58which is exposed to the phase carrying the substance(s) whose reaction is to be catalyzed.

If the substrate of layer54is an electronic conductor (i.e., a metal), the layer56is not necessary, but may be present or useful in certain applications of the present invention.

Conductors/electrodes60,62, and64may be provided for supplying the AC and DC current from the control device50to the layers54,56, and58, respectively.

In the example embodiment shown inFIG. 4, current/voltage are applied between the layers54,56, and58in a three-terminal configuration, in a manner consistent with that described above in connection withFIG. 3.

It should be appreciated thatFIG. 4shows three layers54,56, and58whileFIG. 3shows only an electroconductive support12and a catalyst layer14. Further, it should be appreciated that the control device50and programmable control unit52ofFIG. 4are equivalent to the control unit32ofFIG. 3. The remaining elements ofFIG. 3, such as, for example, the polarization impedance measuring unit26, the current control unit28, AC sensors16, the heater36, the heater control unit34, and interface30, may also be used with the structure shown inFIG. 4to the same or nearly the same effect. In fact, where the substrate of layer54ofFIG. 4is an electronic conductor and layer56is not used, theFIG. 4embodiment becomes substantially similar to that ofFIG. 3.

In an example embodiment of the present invention, an asymmetrical alternating current may be provided to the catalyst layer58(e.g., via conductor64). The polarization impedance of the catalyst layer may be monitored (e.g., by polarization impedance measuring unit26as discussed above in connection withFIG. 3). The polarization impedance may be controlled by varying the asymmetrical alternating current supplied to the catalyst layer58(e.g., by control unit50). The control processes discloses in U.S. Pat. No. 7,325,392 (i.e., controlling the catalytic enhancement via the values of the polarization impedance Rp(ohm)) can be applied to the oxidation of soot generated by the operation of a diesel engine, or from incomplete combustion in a coal-operated heating installation (e.g., in a power plant). As used herein the term “asymmetrical alternating current” is defined to mean an alternating current whose amplitude of the positive part of the cycle (voltage or current) is different from the amplitude of the negative part of the cycle (voltage or current), and can be defined by its asymmetry factor. The asymmetry factor is the ratio of the larger amplitude of the cycle to the smaller amplitude of the cycle. The role of the asymmetrical alternating current is to displace the migration of the interfacial charged species to/or away from the interface at the time scales determined by the (variable) frequency of the asymmetrical alternating current.

In accordance with an example embodiment of the present invention, soot that has built up on the catalyst layer may be eliminated. In particular, in such an example embodiment, carbon may be eliminated by forcing its oxidation through pumping oxygen from a substrate under DECAN conditions, or favoring the oxidation reaction under steam reforming conditions, in an excess of water. Sensing of the onset of soot deposition can be accomplished via examination of the matrix of values of the interfacial impedance: such as, for example, the patterns of the change of the phase angle and of the polarization resistance, which tend to become indeterminate and scattered. The onset of this scattering accompanies the onset of the carbon (soot) deposition, and can be used as a trigger for the application of an example embodiment of a soot oxidation scheme in accordance with the present invention.

Thus, in accordance with example embodiments of the present invention, oxygen may be provided the catalyst layer58to generate an oxidation reaction for eliminating carbon particles from the catalyst layer58. Alternatively or additionally thereto, one of water and steam may be provided to the catalyst layer58to enhance the oxidation reaction.

The catalyst layer58(together with layers56and/or layer54) may be applied to a catalytic reactor. The catalytic reactor may be built around a filter which retains the carbon particles. The deposition of the carbon particles on the catalyst layer58may be monitored. The monitoring of the deposition of the carbon particles may comprise monitoring at least one parameter which describes an interfacial impedance of the catalyst layer58and determining an amount of the carbon particles deposited on the catalyst layer as a function of values of the at least one monitored parameter. For example, the at least one monitored parameter may comprise at least one of the monitored polarization impedance and a phase angle of the interfacial impedance.

Catalyst regeneration may also be achieved in accordance with an example embodiment of the present invention by utilizing a matrix of current and voltage fluctuations, simultaneous (optionally) with a heating profile, which may all be monitored via the measurement of the Rpand phase angle distribution. The effectiveness of the catalyst regeneration is evaluated by the value of the Rp(which has to return to a value as close as possible to the value range characterizing the fresh, unused catalytic system) and the phase angle distribution (the phase angle has to be as close to zero as possible). In other words, the polarization impedance will have a very low capacitive component; for example, phase angle values between −5 degrees and +5 degrees will be considered appropriate for catalyst regeneration within the scope of the present invention

Additional factors assisting in the regeneration of the catalyst may be water vapor injection and the monitored variation of the partial pressure of oxygen in the carrier gas. Such variations in the partial pressure of oxygen can be achieved by methods well known in the prior art.

Thus, in accordance with example embodiments of the present invention, at least one of an amplitude and a phase of the asymmetrical alternating current may be varied (e.g., by control unit50) in order to regenerate the catalyst layer58. For example, the at least one of the amplitude and the phase of the asymmetrical alternating current may be varied to bring the polarization impedance to a value within a predetermined range of values when the polarization impedance value falls outside of this predetermined range. This predetermined range may be a range of values around an original polarization impedance value of the catalyst layer58prior to use.

Further, the at least one of the amplitude and the phase of the asymmetrical alternating current may be varied to achieve a phase angle of an interfacial impedance of the catalyst layer58which is within a range of between approximately −5 degrees and +5 degrees.

In another example embodiment of the present invention, the application of at least one of water, oxygen, and heat to the catalyst layer58may be controlled to enhance the regeneration of the catalyst layer58.

Further, a partial pressure of oxygen in a carrier gas applied to the catalyst layer58may be controlled (varied) in order to enhance the regeneration of the catalyst layer58.

An alternate example embodiment of the present provides a further method for controlling a catalytic process. In such an example embodiment, monitoring a polarization impedance of the catalyst layer58is monitored (e.g., using polarization impedance measuring unit26). Additionally, at least one of an amount of water and an amount of oxygen applied to the catalyst layer may be controlled.

In such an example embodiment, an alternating current may be applied to the catalyst layer58and the polarization impedance may be controlled by varying the alternating current.

The method may further comprise varying at least one of a phase and an amplitude of the alternating current and/or controlling the at least one of the amount of the water and the amount of the oxygen applied to the catalyst layer58to provide at least one of oxidation of carbon particles on the catalyst layer and regeneration of the catalyst layer58.

In addition, an amount of heat applied to the catalyst layer may be controlled in order to further control the regeneration of the catalyst. The heat may be applied using heater36controlled by heater control unit34(shown inFIG. 3), which may be responsive to control signals from control unit50.

The amount of the oxygen may be controlled by varying a partial pressure of oxygen in a carrier gas applied to the catalyst layer58.

The deposition of the carbon particles on the catalyst layer58may be monitored. The monitoring of the deposition of the carbon particles may comprise monitoring at least one parameter which describes an interfacial impedance of the catalyst layer58and determining an amount of the carbon particles deposited on the catalyst layer as a function of values of the at least one monitored parameter. For example, the at least one monitored parameter may comprise at least one of the monitored polarization impedance and a phase angle of the interfacial impedance.

In a further example embodiment of the present invention, the water may be heated to generate steam. In such an example embodiment, the controlling of the amount of the water applied to the catalyst layer58comprises controlling an amount of steam applied to the catalyst layer.

When regenerating the catalyst58, the at least one of the amplitude and the phase of the alternating current may be varied to return the polarization impedance to a value within a predetermined range of values when the polarization impedance value falls outside of this predetermined range. The predetermined range may be a range of values around an original polarization impedance value of the catalyst layer58prior to use.

In addition, when regenerating the catalyst58, the at least one of the amplitude and the phase of the asymmetrical alternating current may be varied to achieve a phase angle of an interfacial impedance of the catalyst layer which is within a range of between approximately −5 degrees and +5 degrees.

In one example embodiment, the alternating current may comprise an asymmetrical alternating current.

The catalyst layer58may be applied to a catalytic reactor. The catalytic reactor may comprise a filter which retains the carbon particles. If the catalytic reactor is built as a filter, this will make sure that the carbon-based particles are retained by the filter, and approximately 98-99 mass % of the soot can be oxidized to CO2.

The controlling of the at least one of the amount of water and the amount of oxygen applied to the catalyst layer58may comprise controlling an amount of steam applied to the catalyst layer. The steam may be wet steam or dry steam, depending on the particular application.

The controlling of the amount of the oxygen applied to the catalyst layer58may comprise controlling environmental oxygen levels present in the exhaust stream, for example by controlling an amount of water or steam injected into the exhaust stream.

A local sensing function is provided in accordance with an example embodiment of present invention, which senses the matrix above, including the values of Rpand phase angle distribution (e.g., using polarization impedance measuring unit26). The matrix is correlated with the gas composition (for instance, the amounts of NOx, CO and other components) and its variations. Brief (10−4−1 second) step functions of applied current/voltage between the working electrode (e.g., electrode64of the catalyst58inFIG. 4) and the auxiliary electrode (e.g., electrode60or electrode62), followed by a Fast Fourier Transform (FFT) analysis of the pattern of the response of the polarized catalytic interface measured between the working and the reference electrodes, provide a unique fingerprint, that can be assigned to a specific composition of the phase in contact with the catalyst. These compositional changes can be relayed to the central computer that controls the operation of the engine (i.e., an engine ECU), for the real-time adjustment of the parameters controlling the operation of the engine: ignition parameters, valve timing, and the like. This application is not limited to the operation of Otto or Diesel engines; the operation of turbine engines can be controlled as well in accordance with the composition of the exhaust gases.

This application does not require a separate sensor. The sensing function is performed by the hardware and the software described above and shown inFIGS. 3 and 4(e.g., electronic control device50, polarization impedance measuring unit26).

With an example embodiment of the present invention, the functionality of, for example, systems including multiple phase and/or multi-functional catalysts, can be achieved by a system using only a single-phase catalyst (built as described in connection withFIG. 4above), but on electrically separated substrates. Each electrically independent section of a stack can be polarized differently, and can thus be controlled to perform different functions (e.g., reduction of NOx in one section, oxidation of carbon monoxide to carbon dioxide in another section, or oxidation of unreacted hydrocarbons in a third section).

Therefore, the same material can perform different functions in different areas of the catalytic reactor. This functionality can be combined with the sensing functions described in above. The externally programmable control unit52(FIG. 4) can effect variations in functionality from one area to another, as required.

The control methods discussed above can also be applied to control of the operation of fuel cells. Example embodiments of the present invention for controlling fuel cells in accordance with the present invention is shown inFIGS. 5aand5b. It is known that the current generated by a fuel cell60is maximized when the mass and charge transfer across the MEA (membrane-electrode assembly) is maximized. The polarization resistance is minimized under these conditions. The fuel cell60ofFIGS. 5aand5bis shown as having an two catalyst layers66, an electrolyte layer68therebetween, and a respective catalyst support70.

In accordance with an example embodiment the present invention, for a maximum yield, a fuel cell60must be driven (any fuel cell type is included here) towards an operation scheme driven by the criterion of minimizing the Rpand achieving a narrow phase angle distribution, as close as possible to zero.FIG. 5ashows an example embodiment of the present invention where the measurements and control of the fuel cell are carried out using a two electrode configuration (catalyst-to-catalyst layer) with a working electrode, WE and counter-electrode, CE.FIG. 5bshows an alternate embodiment of the present invention utilizing a four electrode configuration with two electrodes for each compartment, one electrode CE connected to the catalyst layer, and the other electrode RE connected to the surface of the electrolyte membrane in direct contact with the environment of the respective compartment of the fuel cell.

In both of the above-described example embodiments, the signals from electrodes CE and RE are measured by an Electronic Control Device62similar in function with that described above in connection withFIGS. 3 and 4. The processing of the signal and the commands for driving the operation of the fuel cell are functions which may be performed by a Control Unit64similar in function with that described above in connection withFIG. 4.

When soot is deposited on the catalyst layer under an electric field during the control processes described above (known as carbon deposition, which is undesirable, as discussed above), it was discovered that the deposited layer, which macroscopically looks like an amorphous black powder, was found under electron microscopic examination to possess the structural characteristics of fullerenes and nanotubes, as well as nanoparticles. It was further found that the growth of the individual structured particles under the dominant electric field can lead to different types of deposits. In particular, it was found that if one conducts a process under conditions known as conducive to carbon deposition, but also under using the DECAN process described above, the result is an interfacial layer of nanotubes, fullerenes, and/or nanoparticles.

However, if the particles are not deposited under an electric field (e.g., with passive catalytic methods), they are just a mix of different types of carbon, which cannot be separated from each other and are undesirable in catalytic systems because they obstruct the path of reacting species to the catalytic sites.

Accordingly, in a further embodiment of the present invention, the control processes described above may tailored to control the characteristics of the carbon particles deposited on the catalyst layer. For example, the control process may advantageously be used to deposit carbon particles on the catalyst layer in the form of carbon nanotubes, fullerenes, and/or nanoparticles. Accordingly, methods and apparatus for controlling the deposition of carbon particles on a catalyst layer are also provided in accordance with the present invention.

In one example embodiment, a method for controlling a catalytic layer deposition process is provided. As shown inFIG. 6, a feed stream112containing a carbon source is provided to the catalyst layer114. An asymmetrical alternating current is provided (e.g., from electronic control device120) to a catalyst layer114. A polarization impedance (Rp) of the catalyst layer is monitored. In order to monitor the polarization impedance, the electronic control device120may include means for determining the applied current and voltage. The determination of the polarization impedance from the sensed current is explained in detail in commonly-owned U.S. Pat. No. 7,325,392. Alternatively, the polarization impedance may be monitored by polarization impedance measuring unit26as discussed above in connection withFIG. 3. The polarization impedance may be controlled by varying the asymmetrical alternating current from electronic control device120. Controlling of the polarization impedance provides control over the structure and amount of carbon particles deposited on the catalyst layer114(in the form of a deposited layer115).

The controlling of the polarization impedance may comprise correlating the time variation of the polarization impedance with the thickness and the nature of the deposited layer115. As an example, one practical way to achieve this goal is to correlate the set of currently measured Rpvalues to a database124linking the polarization impedance value with data regarding at least one of the chemical nature, structure and average value for ratios of deposit volume/unit of surface area, and adjusting the deposition and polarization conditions via a feedback system/loop which may include electronic data evaluating the real time variation of the value of the partial pressure of oxygen applied to the catalyst layer114. The oxygen may be applied to the carrier layer in the form of a carrier gas119containing oxygen. The polarization impedance may be adjusted based on the monitoring of the partial pressure of oxygen in order to enhance the deposition of the carbon particles on the catalyst layer. The determining of the partial pressure of oxygen may also be achieved via the electronic control device120as a function of a voltage measurement. For example, a monitoring of the partial pressure of the oxygen may comprise monitoring an interfacial impedance of the catalyst layer114. The partial pressure of oxygen at a level of the catalyst layer114may then be determined as a function of the interfacial impedance. Alternatively, the polarization impedance of the supported catalyst layer114may be monitored as discussed above, and the partial pressure of oxygen at the level of the catalyst layer114may be determined as a function of the monitored polarization impedance (e.g., achieved via the electronic control device120).

The catalyst layer114may be supported on or in close contact with a solid electrolyte (support116). For example, the catalyst layer114may comprise, platinum, semiconducting oxides, other semiconducting materials, etc., which are supported or are in close contact to a solid electrolyte116(examples of solid electrolytes include, but are not limited to: stabilized zirconia, stabilized bismuth oxide, different forms of beta alumina, Nafion; and the like) or a mixed conductor.

In order to apply the alternating current to the catalyst layer114, three electrodes may be provided as shown inFIG. 7. For example, a reference electrode140may be applied to the solid electrolyte layer116, a counter electrode142may be applied to the solid electrolyte layer116, and a working electrode144may be applied to the catalyst layer114.

Experimentation has shown that carbon deposition occurs in such systems as described above, under reducing conditions. Surprisingly, it was found that in the presence of a local electric field produced by the control processes described herein, the product at the three-phase interface consists mostly or exclusively of carbon nanotubes, fullerenes, and/or nanoparticles from the deposited carbon particles. These deposits115can be visualized using, e.g., an electron microscope and their structure can be determined using, e.g., electron diffraction or other adequate techniques.

The feed to the interface consists of at least the following components:

A) a feed stream112comprising a carbon source (e.g., a mix of CO, CO2, hydrocarbons, oxygenated hydrocarbon-derivatives, organic compounds, and the like, whether gaseous, or liquid); and

B) (optionally) a water or steam source (e.g., which may be included in feed stream112or separately provided in a secondary water or steam feed118), depending on the temperature at which the process is conducted.

The process may work in gas phase or in the liquid phase—the ionic conductivity of the solid electrolyte116appears to be a determining factor in this regard. The values of the ionic conductivity are situated within the range of 1 to 10−4ohm−1*cm−1(most useful), but can be situated outside this range. The limits of the range depend on the specific electronic equipment used for the measurement and the control of the process.

In a further example embodiment as shown inFIG. 8, the feed stream112may be introduced into a chamber222containing the catalyst114. The chamber222may comprise a tubular reactor. The alternating current may be controlled by an electronic control device120. The feed stream112may be introduced to the chamber222from a tank211. Water or steam118may be introduced to the chamber222from a pump217.

The method may further comprise extracting and/or electrically pumping oxygen from the catalyst layer114(e.g., via pump224) to generate a reduction reaction for initiating or enhancing the deposition of carbon particles115onto the catalyst layer114.

The rate or structure of the carbon particles deposited on the catalyst layer114may be monitored (e.g., via the electronic control device120). The monitoring of the deposition of the carbon particles may comprise monitoring at least one parameter which describes an interfacial impedance of the catalyst layer114and determining an amount of the carbon particles115deposited on the catalyst layer114as a function of values of the at least one monitored parameter. For example, the at least one monitored parameter may comprise at least one of the monitored polarization impedance and a phase angle of the interfacial impedance.

In a further example embodiment of the present invention, at least one of an amplitude and a phase of the asymmetrical alternating current may be varied by the electronic control device120in order to control the characteristics of the deposited layer115. For example, the at least one of the amplitude and the phase of the asymmetrical alternating current may be varied to bring the polarization impedance to a value within a predetermined range of values when the polarization impedance value falls outside of this predetermined range. This predetermined range may be a range of values around an original polarization impedance value of the catalyst layer114prior to use (e.g., a clean catalyst layer).

Further, the at least one of the amplitude and the phase of the asymmetrical alternating current may be varied by the electronic control device120to achieve a phase angle of an interfacial impedance of the catalyst layer114which is within a range of between approximately −10 degrees and +10 degrees.

In another example embodiment of the present invention, the application of at least one of water, steam, oxygen, and heat to the catalyst layer114may be controlled to control the deposition of the carbon layer on the catalyst. For example, water or steam118may be introduced into chamber222via pump217. Oxygen119may be introduced into chamber222via pump221. Heat may be applied to the catalyst layer114via a heating element234controlled by a temperature control unit236.

Further, a partial pressure of oxygen in a carrier gas119applied to the catalyst layer114may be controlled (varied) in order to enhance the deposition of carbon on the catalyst layer.

The method may further comprise varying at least one of a phase and an amplitude of the alternating current and/or controlling the at least one of the amount of the water, steam, and/or oxygen applied to the catalyst layer114or deposited layer115to provide at least one of a reduction of at least one of the liquid phase and the gas phase in contact with the catalyst layer114, and to stimulate growth of the deposited layer115.

In addition, an amount of heat applied to the catalyst layer may be controlled (e.g., via temperature control unit236) in order to further control the structure and/or thickness of the deposited layer115.

In a further example embodiment of the present invention, the water may be heated to generate steam. In such an example embodiment, the controlling of the amount of the water applied to the catalyst layer114may comprise controlling an amount of steam applied to the catalyst layer114.

The method may further comprise harvesting nanotubes, fullerenes, and/or nanoparticles from the deposited carbon layer115. For example, the deposition interface can be viewed as a filter, and the nanotubes, fullerenes, and/or nanoparticles can be removed from the filter using known chemical engineering methods for removing valuable precipitates from a filter (for example, vibratory removal, removal with the help of a fluid phase (e.g., water introduced from pump217) which washes the deposits115into a suitable particulate filter226, and the like).

After harvesting of the nanotubes, the catalyst layer114may be regenerated as discussed above.

The present invention may also be expanded to control deposition of nanotubes, fullerenes, or nanoparticles made from other materials of electronic interest (e.g., silicon/doped silicon, silicon carbide, gallium arsenide, niobium, boron and the like).

It should now be appreciated that the present invention provides advantageous methods and apparatus for controlling catalytic processes, including soot elimination, catalysts regeneration, and carbon deposition in the form of carbon nanotubes, fullerenes, and/or nanoparticles.

Although the invention has been described in connection with various illustrated embodiments, numerous modifications and adaptations may be made thereto without departing from the spirit and scope of the invention as set forth in the claims.