Catalytic Oxidative Dehydration of Butanol Isomers: 

1-Butanol, 2-Butanol, and Isobutanol

by Ivan C. Lee, Jeffrey G. St. Clair, and Adam S. Gamson

ARL-TR-5721 September 2011

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Army Research Laboratory

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ARL-TR-5721 September 2011

Catalytic Oxidative Dehydration of Butanol Isomers: 

1-Butanol, 2-Butanol, and Isobutanol

Ivan C. Lee, Jeffrey G. St. Clair, and Adam S. Gamson

Sensors and Electron Devices Directorate, ARL

Approved for public release; distribution unlimited. 
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Catalytic Oxidative Dehydration of Butanol Isomers: 1-Butanol, 2-Butanol, and 

Isobutanol

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Ivan C. Lee, Jeffrey G. St. Clair, and Adam S. Gamson

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14. ABSTRACT

The catalytic production of economically important four-carbon olefins was achieved through catalytic oxidative dehydration 

of 1-butanol, 2-butanol, and isobutanol using a millisecond contact time reactor. Both alumina foam and rhodium-alumina 

foam catalysts convert these four-carbon alcohols into four-carbon olefins, with contact time equal to 25 ms over a wide range 

of equivalence ratios (φ) from 0.176 to 6.338 (or C/Oair ratio from 0.0659 to 2.11). The cracking of the carbon backbone was 

found to be minimal. A mixture of butene isomers was obtained due to the isomerization of the carbocation intermediates. 

The degree of this isomerization was determined by analyzing the ratios of butenes/(total olefins), 1-butene/2-butene, cis-2-

butene/trans-2-butene, and isobutene/(linear butenes). In addition, a reaction mechanism of the catalytic oxidative 

dehydration of butanol in short contact times was proposed. In this mechanism, the C-O bond of the majority of butanol was 

broken to form olefinic species on the alumina surface. These surface olefinic species would undergo successive oxidation to 

form CO and/or CO2, depending on the availability of oxygen. 

15. SUBJECT TERMS

Butanol, catalysis, renewable energy

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Ivan C. Lee

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iii

Contents

List of Figures v

List of Tables v

1. Introduction 1

2. Experimental 2

2.1 Materials..........................................................................................................................2

2.2 Reactor Setup and Operation...........................................................................................2

2.3 Product Gas Analysis ......................................................................................................3

2.4 Equilibrium Calculations of 1-butanol Conversion.........................................................4

3. Results 5

3.1 Equilibrium Calculations.................................................................................................5

3.2 Conversion.......................................................................................................................5

3.3 Olefins Selectivity and Distribution................................................................................7

3.4 CO Selectivity .................................................................................................................9

3.5 CO2 Selectivity ................................................................................................................9

3.6 Paraffins Selectivity ........................................................................................................9

4. Discussion 13

4.1 Conversions...................................................................................................................13

4.2 Dehydration vs. Dehydrogenation.................................................................................13

4.3 Olefins Distribution.......................................................................................................14

4.4 Oxidation Over Rh/Al2O3..............................................................................................16

4.5 Cracking Reactions........................................................................................................16

4.6 Proposed Reaction Mechanism .....................................................................................17

5. Conclusions 17

6. References 18
iv

Supplemental Materials 20

List of Symbols, Abbreviations, and Acronyms 24

Distribution List 25
v

List of Figures

Figure 1. Experimental setup for olefin production........................................................................3

Figure 2. Equilibrium calculations of product selectivity for 1-butanol reaction with oxygen......5

Figure 3. Conversion of butanol isomers with empty tube, blank alumina foam, -alumina 

coated foam, and Rh/alumina foam: (a) 1-butanol, (b) 2-butanol, and (c) isobutanol. ............6

Figure 4. Olefins selectivity for catalytic oxidative dehydration of butanol isomers with 

empty tube, blank alumina foam, -alumina coated foam, and Rh/ alumina foam: 

(a) 1-butanol, (b) 2-butanol, and (c) isobutanol.........................................................................8

Figure 5. Carbon monoxide selectivity for catalytic oxidative dehydration of butanol 

isomers with empty tube, blank alumina foam, -alumina coated foam, and Rh/alumina 

foam: (a) 1-butanol, (b) 2-butanol, and (c) isobutanol............................................................10

Figure 6. Carbon dioxide selectivity for catalytic oxidative dehydration of butanol isomers 

with empty tube, blank alumina foam, -alumina coated foam, and Rh/alumina foam: 

(a) 1-butanol, (b) 2-butanol, and (c) isobutanol.......................................................................11

Figure 7. Paraffins selectivity for catalytic oxidative dehydration of butanol isomers with 

empty tube, blank alumina foam, -alumina coated foam, and Rh/alumina foam: 

(a) 1-butanol, (b) 2-butanol, and (c) isobutanol.......................................................................12

Figure 8. Isomerization of Carbocations from the dehydration of C4 alcohols (19)....................14

Figure 9. Proposed mechanism for the catalytic oxidative dehydration of butanol isomers. .......17

List of Tables

Table 1. Butenes/(Total Olefins) Ratio for reactions of butanol isomers: (a) 1-butanol, (b) 2-

butanol, and (c) isobutanol......................................................................................................20

Table 2. 1-Butene/2-Butenes Ratio for reactions of butanol isomers: (a) 1-butanol, (b) 2-

butanol, and (c) isobutanol......................................................................................................21

Table 3. Cis/Trans Ratio for reactions of butanol isomers: (a) 1-butanol, (b) 2-butanol, and 

(c) isobutanol. ..........................................................................................................................22

Table 4. Isobutene/(Linear Butenes) Ratio for reactions of butanol isomers: (a) 1-butanol, 

(b) 2-butanol, and (c) isobutanol.............................................................................................23
vi

INTENTIONALLY LEFT BLANK.
1

1. Introduction

Butanol is a potential alternative hydrocarbon source for energy and chemical industries because 

it is easily available through fermentation of non-food biomass and wastewater (1–3). 

Dehydration of butanol isomers (1-butanol, 2-butanol and isobutanol) produces butenes, such as 

1-butene, cis-2-butene, trans-2-butene and isobutene, which are highly valuable starting 

materials for other industries to make synthetic fuels, lubricants, and other high value chemicals. 

For example, 1-butene is used in the creation of plastic materials, such as linear low density 

polyethylene. 2-butene isomers are an extremely valuable starting material for lubricants, as 

well as agricultural chemicals (4). In olefin metathesis, 2-butene reacts with ethylene to form 

propylene (5). Isobutene is the starting material for butyl rubber, methyl tert-butyl ether

(MTBE), and isooctane. In addition, synthetic petroleum kerosene (SPK) can be synthesized by 

oligomerization of 4-carbon olefins (6–8). 

The production of olefins from hydrocarbons, as well as other sources, such as biodiesel and C1-

C3 alcohols, is well documented in the literature (9–12). In one such process, ethane autothermally decomposes to form ethylene (9). This process also converts heavier paraffins, such as 

n-octane, into mixtures of olefins (10). A rhodium/cerium catalyst has been proposed in the past 

to convert biodiesel into olefins (11). The catalyst produces mainly two- and three-carbon 

olefins, and has a total olefin selectivity of about 42%. The preferred contact time was no 

greater than 50 ms. In another work, Wanat et al. suggested that alkoxyl species was the surface 

intermediate for olefin production from C1-C3 alcohols (12).

A process for converting dry and aqueous 2-butanol directly to isooctenes was carried out in a 

batch process (13, 14). The butanol conversions were as high as 75%, but the product selectivity 

into the desired iso-octenes was generally very low, creating only a small product yield (yield = 

conversion × selectivity). The same group proposed another process of butene production from 

dry and aqueous 2-butanol in a pressurized batch reactor (15, 16). They were able to achieve 

100% conversion and 100% selectivity of a 70 wt% mixture of butanol with sulfuric acid as a 

catalyst (16). 

Recently, catalytic combustion of 1-butanol in a millisecond contact time reactor has been 

demonstrated (17). The combustion of 1-butanol is extremely exothermic and occurs via the 

process detailed in Equation 1. 

CH3CH2CH2CH2OH + 6 O2  4 CO2 + 5 H2O ΔH = –2713 kJ/mol (1)

This heat production enables the reaction to perform auto-thermally. As a result, the catalytic 

reaction initiates at a temperature as low as 240 °C, and the catalyst temperature rises to 450 °C

or above. It was shown that three distinct regimes exist in the catalytic butanol combustion. The 

product selectivity can be tuned by changing the equivalence ratio (φ), which is the operating 
2

fuel-to-air ratio compared to the stoichiometric value. When the equivalence ratio is less than 1, 

complete combustion occurs with the formation of H2O and CO2 as the major products. In the 

second regime of slightly higher equivalence ratios, the product selectivities of hydrogen (H2)

and carbon monoxide (CO) increase. Finally, further increase in equivalence ratio promotes the 

formation of olefins in an autothermal process. In contrast, traditional dehydration processes

require external heating to maintain catalyst temperatures at about 300–400 °C (18, 19).

In this study, catalytic oxidative dehydration of three butanol isomers including 1-butanol, 2-

butanol, and isobutanol was investigated in a short contact time reactor with residence time of 

25 ms and a pressure drop of less than 10 psig. The product selectivity of each butanol isomer in

a Rh/Al2O3, a γ-Al2O3-coated alumina foam, a blank alumina foam, and an empty tube reactor 

were compared. Based on these results, contributions of homogenous and heterogeneous 

reactions were determined. Then a mechanism of the olefin production and consumption is 

proposed. 

2. Experimental

2.1 Materials

Catalytic oxidative dehydration of 1-butanol, 2-butanol, and isobutanol was investigated using 

three catalysts and an empty reactor tube in this study. All three butanol isomers are of high 

performance liquid chromatography (HPLC) grade or higher. The primary catalyst was 

comprised of a Rh/Al2O3 foam as in previous studies [17, 22]. The catalyst preparation started 

with alumina monolith foam (Vesuvius, 80 ppi, 17 mm diameter, 1 cm thick) that was coated 

with γ-alumina to roughen the foam surface and increase the surface area. Then the foam was 

calcined in a box furnace at 700 °C for 15 h. An aqueous Rh(NO3)3 solution was added to the 

gamma-alumina coated foam, and the resultant foam was calcined in the box furnace at 700 °C 

for another 15 h. The resulting Rh/Al2O3 foam catalyst contained approximately 0.07353 g of 

Rh. The second catalyst is the γ-alumina coated foam without Rh. The third catalyst is a blank

monolith foam. Lastly, the reaction was studied in an empty tube configuration.

2.2 Reactor Setup and Operation

The experimental set-up of the cylinder quartz reactor (2 cm diameter) is shown in figure 1. 

Amounts of nitrogen (N2) and oxygen (O2) gases were controlled with two separate MKS mass 

flow controllers, and the resultant mixture was introduced near the top of the reactor. An amount 

of liquid butanol was delivered through a 1/16 in stanliness steel tubing from a VICI micropump. 

A grounded –tantalum (Ta) mesh and a mixing alumina foam (45 ppi) was placed 1 cm below 

the end of this fuel delivery tube. The catalyst material was placed between other two alumina 

foams (45 ppi) that acted as heat shields, and also served as another mixing layer to ensure 

uniform fuel vapor concentration over the entire catalyst surface. The distance between the 
3

grounded mesh and the top heat shield was 12.5 cm, and this region was surrounded by heating 

tape to assist fuel vaporization and to preheat the catalyst material to the ignition temperature 

(240 °C for Rh/Al2O3 catalyst). The preheat temperature for the other three catalyst 

configurations was between 460–500 °C so that the final catalyst backface temperature was 

comparable to that of the Rh/Al2O3 (table 5 in supplementary materials).

Figure 1. Experimental setup for olefin production.

Initially, the catalyst was preheated to the self-ignition temperature by flowing only N2 and O2

through the preheat region. Once the catalyst reached the self ignition temperature, the liquid fuel 

was electrosprayed in cone-jet mode by creating a voltage difference (~3300 V) between the 

droplet source and a neutral grounded mesh (17, 22). Once the catalyst was ignited, the catalyst 

backface temperature was allowed to reach its steady-state temperature. The effluent gas was 

sent to an ice-water bath, then to the Agilent 4-channel micro gas chromatograph (GC) for 

composition analysis. 

2.3 Product Gas Analysis

The amounts of H2, O2, N2, CO, carbon dioxide (CO2), methane, acetylene, ethane, ethylene, 

propane, propylene, butane, 1-butene, cis-2-butene, trans-2-butene, isobutene, 1,3-butadiene, 1,2-

butadine, pentane, cis-2-pentene, and trans-2-pentene were monitored by an Agilent 4-channel 

micro-GC. Each analysis takes approximately 4 min, and 10 analyses were performed to obtain 
4

the average gas composition. Conversion is defined by carbon balance (equation 2). When all 

the carbon atoms in butanol are converted to the carbon species—including CO, CO2, methane, 

acetylene, ethane, ethylene, propane, propylene, butane, 1-butene, cis-2-butene, trans-2-butene, 

and isobutene—the conversion would be 100%. The carbon selectivity was defined as the 

number of carbon atoms in a product species, divided by the total number of carbon atoms in all 

the product species (equation 3). 

2 C in CO CO Paraffin Olefin Species , , ,

Conversion

C in Alcohol Feed

 



(2)

#C in Species X C atom Selectivity

C in product





(3)

The amounts of oxygenates from the oxidative dehydration of all three butanol isomers over the 

γ-Al2O3-coated foam were determined by analyzing exhaust gas composition with the flame

ionization detector of a GC. A HP-INNOWAX column was employed to quantify polar 

molecules including 1-butanol, 2-butanol, isobutanol, other C1-C3 alcohols (methanol, ethanol, 1-

propanol, 2-propanol), aldehydes (formaldehyde, acetaldehyde, propionaldehyde, 

isobutraldehyde, butanal), and ketones (acetone, 2-butanone). It was found that the concentration 

of the C1-C3 alcohols, aldehydes, or ketones was less than 50 ppm, which corresponded to carbon 

selectivity of less than 0.05%.

2.4 Equilibrium Calculations of 1-butanol Conversion

Gas phase equilibrium calculations of 1-butanol combustion were carried out using the software 

Chemkin Pro Release 15092 from Reaction Design. Such calculations require only the 

thermodynamic properties of each compound considered for the simulation, thus no transport or 

kinetic properties are necessary. The thermodynamic data set originates from Sarathy et al. (20).

The gas and fuel ratios are the same as those used for the reactor. Equivalent ratios from 0.18 to 

6.34 were investigated using a constant temperature and pressure process. The temperature for 

each equivalence ratio matched the backface temperature of the alumina catalyst at that 

equivalence ratio (between 481 °C and 491 °C). The pressure was set at 1 atm. The software 

displays the mole fraction of each constituent of the resulting product gas. Selectivity was then 

calculated using the same methodology that was described in the previous section. By 

comparing the calculated equilibrium product selectivity with the experimental value, the effect 

of short contact time (25 ms) on reaction kinetics can be determined.
5

3. Results

3.1 Equilibrium Calculations

The carbon and H selectivity of 1-butanol homogeneous combustion that has reached 

equilibrium is given in figure 2. At low  values, complete combustion is observed, in that only 

CO2 and water are formed. CO and H2 reached a maximum selectivity at = 3.5, whereas CO2

and water selectivities drop significantly as the equivalence ratio is increased. Methane, the 

other major product, increases in selectivity as the amount of O2 relative to fuel decreases. Other 

compounds were observed, including olefins, but these compounds had negligible selecitivities 

(<0.1%). 

Figure 2. Equilibrium calculations of product selectivity for 1-butanol reaction with O2.

3.2 Conversion

Figure 3 illustrates the conversion of butanol isomers with four different catalyst configurations. 

The alcohol conversion with the empty tube remained small (<25%). Conversions of isobutanol 

and 1-butanol were less than 10% for all equivalence ratios, while the conversion of 2-butanol 

was around 20%. This could suggest that 2-butanol is more reactive than the other two butanol 

isomers in gas phase conversion. In general, the conversion of butanol isomers increases as 

empty tube < blank alumina foam < -alumina coated foam < Rh/alumina foam. 
6

(a)

(b)

(c)

Figure 3. Conversion of butanol isomers with empty tube, blank alumina foam, 

-alumina coated foam, and Rh/alumina foam: (a) 1-butanol, (b) 2-butanol, 

and (c) isobutanol. 
7

3.3 Olefins Selectivity and Distribution

Figure 4 illustrates the carbon selectivity of catalytic oxidative dehydration of butanol isomers. 

In contrast to equilibrium calculations, olefin selectivity generally remains at a high level (>80%) 

at all equivalence ratios for configuration of empty tube, blank alumina foam, and -alumina 

coated foam. This suggested that the contact time of 25 ms was too short to crack the C-C bond 

in the butanol backbone. Cracking reaction will be discussed later. As previously mentioned,

three distinct regimes exist in presence of Rh, and the reactor can be tuned to operate in any 

regime by changing the equivalence ratio. Increasing the equivalence ratio reduces the relative 

amount of O2 in the feed. As is shown in figure 4, olefins selectivity started to increase after  = 

1.42. At  = 4.75, the carbon selectivities of olefins from 1-butanol, 2-butanol, and isobutanol 

were 21.9, 21.6, and 29.0, respectively. Further increase of equivalence ratio enhances olefins 

production. At  = 6.34, the corresponding carbon selectivities of olefins were 39.7, 38.5, and 

46.0, respectively. 

The olefins distribution was analyzed by butenes/(total olefins) ratio, 1-butene/2-butene ratio, 

cis/trans ratio, and (isobutene)/(linear butane) ratio. These ratios for each isomer at all 

equivalence ratios were tabulated in the supplemental materials. It was observed that 

butenes/(total olefins) ratio was generally > 90% in absence of Rh with each butanol isomer at all 

equivalence ratios. The only exception was the 1-butanol reaction in an empty tube, in which the 

butenes/(total olefins) ratio was between 0.520 to 0.716 for 0.176 <  < 6.34. In the empty tube 

configuration, ethylene and propylene were produced from 1-butanol. In the presence of Rh, the 

butenes / (total olefins) ratio for 1-butanol, 2-butanol, and isobutanol reactions were 0.874, 

0.979, and 0.951, respectively.

The preferred butene product was different depending on the butanol isomer. The 1-butene/2-

butene ratio for 1-butanol reaction was > 1 for all catalyst configurations at each  while the 

isobutene/(linear butenes) ratio was always equal to 0. These results indicate that 1-butene was 

the preferred butene product. In contrast, the 1-butene/2-butene ratio for 2-butanol reaction was 

<1 for all catalyst configurations at each  while the isobutene/(linear butenes) ratio was always 

equal to 0. The cis/trans ratio is >1. These indicated that cis-2-butene was the preferred butene 

product from 2-butanol reaction. Finally, the preferred butene product from isobutanol reaction 

was isobutene. The isobutene/(linear butenes) ratio was always >1. 1-butene/2-butene ratio was 

<1, except in the empty tube configuration.
8

(a)

(b)

(c)

Figure 4. Olefins selectivity for catalytic oxidative dehydration of butanol isomers 

with empty tube, blank alumina foam, -alumina coated foam, and Rh/

alumina foam: (a) 1-butanol, (b) 2-butanol, and (c) isobutanol. 
9

3.4 CO Selectivity

Figure 5 illustrates the CO selectivity from the reaction of each butanol isomer. In the absence of 

Rh, the CO selectivity remains low (<7 %). In contrast, the CO selectivity with a Rh/alumina 

catalyst started to rise at  = 1.42 and reached a maximum at  = 3.50. The maximum CO 

selectivities for 1-butanol, 2-butanol, and isobutanol reactions were 69.8, 68.1, and 72.7, 

respectively. Then the CO selectivity started to fall for  > 3.50. 

3.5 CO2 Selectivity

As shown in figure 6, the CO2 selectivity for the reaction of each butanol isomer in the absence 

of Rh was <20%. In the presence of Rh, the CO2 selectivity was 100% for the reaction of each 

butanol isomer at  ≤ 0.939. As the equivalence ratio further increased, the CO2 selectivity 

dropped gradually. 

3.6 Paraffins Selectivity

Figure 7 illustrates the paraffins selectivity. It was found that paraffins were formed only with 

the Rh/alumina catalyst when  ≥ 4.75 for 1-butanol and 2-butanol, as well as  ≥ 3.50 for 

isobutanol. The only paraffin was methane, and there was no ethane, propane, or butane. It was 

also observed that propylene was formed at the same time with methane.
10

(a)

(b)

(c)

Figure 5. CO selectivity for catalytic oxidative dehydration of 

butanol isomers with empty tube, blank alumina foam, -alumina coated 

foam, and Rh/alumina foam: (a) 1-butanol, (b) 2-butanol, and (c) isobutanol. 
11

(a)

(b)

(c)

Figure 6. CO2 selectivity for catalytic oxidative dehydration of butanol 

isomers with empty tube, blank alumina foam, -alumina coated foam, 

and Rh/alumina foam: (a) 1-butanol, (b) 2-butanol, and (c) isobutanol. 
12

(a)

(b)

(c)

Figure 7. Paraffins selectivity for catalytic oxidative dehydration of butanol 

isomers with empty tube, blank alumina foam, -alumina coated foam, 

and Rh/alumina foam: (a) 1-butanol, (b) 2-butanol, and (c) isobutanol. 
13

4. Discussion

4.1 Conversions

By comparing the conversion of the reactor with (1) no foam catalyst, (2) blank alumina foam, 

(3) -alumina coated alumina foam, and (4) the coated alumina foam with Rh added, the relative 

contributions of various homogeneous and heterogeneous reactions were elucidated. The 

conversion to known products is low in the empty tube experiments, implying a small 

contribution from homogeneous reactions at reaction temperatures below 510 °C. In comparison 

to empty tube experiments, the conversion improved significantly with the presence of a solid 

phase of alumina or Rh/alumina. The improvement of conversion by the presence of the blank 

alumina foam indicates surface reactions dominate in the conversion of butanol isomers. The 

contribution of heterogeneous reactions on alumina was further investigated by changing the 

surface area of the alumina. For instance, the conversion of isobutanol was over 60% in the 

presence of the blank alumina foam. The isobutanol conversion was further improved to 80% by 

adding a coating of -alumina onto the alumina foam. A similar trend in conversion was 

observed with 1-butanol conversion. For 2-butanol, the conversion improvement from the -

alumina coating is minimal, which again suggests that 2-butanol is so reactive that the 

conversion is not reaction-limited but mass transfer-limited. In general, the conversion increases 

in the order of empty tube < blank alumina foam < -alumina-coated alumina foam < Rh/-

alumina foam. This supports the implication that the contribution of homogenous (gas phase) 

reaction is relatively small compared to heterogeneous (surface) reactions. 

4.2 Dehydration vs. Dehydrogenation

In the absence of Rh in the catalyst, four-carbon olefins were the major products at all 

equivalence ratios for all three isomers (figure 4). Since a minimal amount of H2 gas was

detected, it implied that dehydration (equation 4) of butanol isomers occurred with negligible 

dehydrogenation (equation 5) in the empty tube, over the blank alumina foam and γ-alumina 

foam.

C4H9OH  C4H8 + H2O (4)

C4H9OH  C4H8O +H2 (5)

This finding is consistent with a previous study (21), which showed that dehydration is dominant 

over the dehydrogenation at a higher temperature (>250 °C).

In the presence of Rh, the olefins’ selectivity remained <1% for  < 2.0, which indicates that 

either there was an alternative pathway other than equations 4 or 5, or the olefins formed through 

equation 4 were too reactive in the presence of Rh. The olefins’ selectivity increased with higher 
14

equivalence ratios. Since the olefins’ selectivity depended on O2 content, the oxidation of olefins 

could be the reason why the selectivity was negligible at < 2.0 and increases for  >2.0.

4.3 Olefins Distribution

In this study, it was assumed that the reaction underwent unimolecular elimination (E1)

mechanism; therefore, carbocation was the intermediate of the reaction. According to Macho et 

al., dehydration of C4 alcohol would produce a corresponding carbocation intermediate, followed 

by isomerization of this carbocation producing olefins (figure 8) (19). In this section, the focus is 

on the olefin distribution using the -alumina-coated foam and the Rh/Al2O3 catalyst. The olefin 

distribution using the empty tube and the blank foam can be found in the supplemental materials. 

First, the degree of C-C bond scission was determined by analyzing the butenes/(total olefins) 

ratio (table 1 in Supplemental Materials). The degree of skeletal isomerization of the 

carbocations could be indicated by the 1-butene/2-butene ratio (table 2 in Supplemental 

Materials) and the isobutene/(linear butene ratio) (table 4 in Supplemental Materials). In 

addition, the cis/trans ratio would provide information on the surface geometric effect (table 3 in 

Supplemental Materials).

Figure 8. Isomerization of Carbocations from the dehydration of C4 alcohols (19).

In catalytic oxidative dehydration of 1-butanol, the primary carbocation (Structure I in figure 8) 

was formed initially. There was minimal thermal cracking along the carbon backbone since 88–

99% of the olefins produced were butene isomers. Then the degree of isomerization of the 

initially formed carbocation was determined by 1-butene/2-butenes ratio (A/B) and 

isobutene/(linear butenes) ratio. It was found that the isomerization from primary carbocation 

CH2

+

CH

+

Structure I

Structure II

Structure III

CH

+

Structure IV

CH2

+

Structure V

C

+
15

(Structure I) to secondary carbocation (Structure II or III) was between 42% and 28%, depending 

on the catalyst configuration and equivalence ratio (equation 6): 

PS= 1/(1+A/B), (6)

where PS represents the degree of isomerization from primary to secondary carbocation, and A/B 

represents the 1-butene/2-butenes ratio. The 1-butene/2-butenes ratio was determined to be 

between 1.4 and 2.6. Although trans-2-butene was generally believed to be more stable than cis2-butene in gas phase reaction due to steric hindrance, cis carbocation was found to be the 

preferred surface orientation, as indicated by cis/trans ratio greater than 1. Since the 

isobutene/(linear butenes) ratio was zero, there was no isomerization to tertiary carbocation 

(Structure V).

Similarly, secondary carbocation (Structure II or III) was formed initially during catalytic 

oxidative dehydration of 2-butanol. Like 1-butanol, there was minimal thermal cracking of the 

hydrocarbon backbone since the typical butenes/(total olefin) ratio was 0.98-0.99. It was found 

that about 33–37% of the secondary carbocation isomerized to form the primary carbocation 

(equation 7):

SP = (A/B) / (1+A/B), (7)

where SP represents the degree of isomerization from secondary carbocation to primary 

carbocation. The 1-butene/2-butenes ratio (A/B) was between 0.49 and 0.59, depending on the 

catalyst configuration and equivalence ratio. Again, the cis-carbocation was the preferred surface 

orientation over the trans-carbocation. Since the isobutene/linear butenes ratio was zero, there 

was no isomerization to tertiary carbocation. 

Finally, the branched carbocation intermediate (Structure IV) from catalytic oxidative 

dehydration of isobutanol isomerizes to all other four carbocation structures. There was minimal 

thermal cracking since the butenes/(total olefins) ratio was between 0.98 and 0.99. About 74–

80% of branched carbocation (Structure IV) isomerized to tertiary carbocation (Structure V) 

according to equation 8:

BT = (i/L)/(1+i/L), (8)

where i/L represents isobutene/(linear butenes) ratio with typical values of 2.9-3.9, depending on 

the catalyst configuration and equivalence ratio. The remaining 20–26% of branched 

carbocation isomerized to form secondary carbocation. Since the cis/trans ratio was greater than 

1 with alumina-coated foam, the cis-carbocation was the preferred orientation. In contrast, the 

trans-carbocation was preferred on Rh/alumina catalyst. Moreover, the typical 1-butene/2-

butene ratio was 0.73-0.92. According to equation 7, about 42–48% of the secondary 

carbocations (Structure III and III) isomerized to primary carbocation (Structure I).
16

4.4 Oxidation Over Rh/Al2O3

The CO selectivity provided an evidence for the oxidation of olefins over the Rh. The empty 

tube, blank alumina foam, and the γ-alumina-coated foam produced a negligible amount of CO 

(<10% selectivity) at all equivalence ratios for all three butanol isomers. However, partial 

oxidation of olefins occurred over the Rh/alumina catalyst for  > 0.94.

C4H8 + 2 O2  4 CO + 4 H2 (9)

The CO2 selectivity confirmed that oxidation reaction occurred. In the experiments with an 

empty tube, blank alumina, and the -alumina-coated foam, CO2 selectivity of each butanol 

isomer reached a maximum of about 15% at  = 1.42. This indicates that there were some 

combustion activities in the gas phase. In contrast, the CO2 selectivity of each butanol isomer 

over Rh/alumina catalyst was 100% for φ ≤ 0.94. This suggested that the C4H8 from dehydration 

(equation 4) was fully oxidized at high enough O2 concentration through equations 9 and 10. 

CO + O2  CO2 (10)

When > 0.94, there was not enough O2 to fully combust the olefins. Therefore, CO2 selectivity 

dropped gradually with a gradual increase in CO selectivity. When  > 3.50, there was not 

enough O2 to partial oxidize the olefins. Therefore, CO selectivity dropped gradually and olefins 

selectivity increased simultaneously.

4.5 Cracking Reactions

In absence of Rh, no paraffin was formed. However, a small amount of all isomers was cracked 

to produce a C3 fragment and a C1 fragment in the presence of Rh at  > 3.5. The absence of C5 

fragment (pentane or pentenes) indicated that there was no cracking from a C8 dimer 

intermediate. The C3 fragment was propylene, not propane. No ethane was observed, but 

methane was formed. Since the carbon selectivity of propylene was approximately three times

than that of methane, the following cracking reaction may occur on an H-covered Rh surface to 

produce both propylene and methane when O2 is limited:

C4H8 + 2 H  C3H6 + CH4 (11)

In contrast, equilibrium calculations have shown that the cracking reactions of butanol produced 

only methane at high  (>1.4), which is different from our experimental results. This can be 

explained by the effect of contact time. Our results were obtained at contact time of 25 ms,

which could be too short to achieve equilibrium composition. This explanation is consistent with 

the study on isobutanol conversion with different contact times (22), in which the propylene 

selectivity increased from 4.4% to 14.3%, as the contact time increased from 25 ms to 125 ms. 

This demonstrates that C-C bond scission is favored with a longer contact time. As also shown 

in equilibrium calculations, all C-C bonds would have been broken to form CO, CO2, and 

methane at equilibrium (i.e., contact time approaches infinity).
17

4.6 Proposed Reaction Mechanism

From this study, a mechanism of catalytic oxidative dehydration of butanol is proposed in figure 

9. The majority of butanol reacts to produce olefins on the alumina surface, which involves C-O 

bond scission. At the same time, the contribution of gas phase reaction is smaller. Isomerization 

of the carbocations results in a mixture of butene isomers. Then the olefins are oxidized on the 

Rh in the presence of O2 to produce CO and/or CO2, depending on the availability of O2.

Adsorption geometry of the surface species will be the subject of future studies.

Figure 9. Proposed mechanism for the catalytic oxidative dehydration of butanol isomers.

5. Conclusions

Catalytic oxidative dehydration of 1-butanol, 2-butanol, and isobutanol was investigated with 

short contact time (25 ms). Product selectivity was compared with several configurations

including empty tube, blank alumina foam, -alumina-coated foam, and addition of Rh. It was 

found that the majority of butanol dehydrates to form four-carbon olefinic species on the alumina 

surface. Depending on the availability of O2, these olefins were further oxidized to form CO 

and/or CO2.
18

6. References

1. Napoli, F.; Olivieri, G.; Russo, M. E.; Marzocchella, A.; Salatino, P. Butanol Production by 

Clostridium Acetobutylicum in a Continuous Packed Bed Reactor. Journal of Industrial 

Microbiology & Biotechnology 2010, 37, 603–608.

2. Lee, S. Y.; Park, J. H.; Jang, S. H.; Nielsen, L. K.; Kim, J.; Jung, K. S. Fermentative Butanol 

Production by Clostridia. Biotechnology and Bioengineering 2008, 101, 209–228.

3. Zverlov, V. V.; Berezina, O.; Velikodvorskaya, G. A. Bacterial Acetone and Butanol 

Production by Industrial Fermentation in the Soviet Union: Use of Hydrolyzed Agricultural 

Waste for Biorefinery. Appl Microbiol Biotechnol 2006, 71, 587–597.

4. Hasenberg, D. M.; Refvik, M. D.; Matson, M. S. Process to Isomerize 1-butene to 2-butene. 

U.S. Patent No.: U.S. 6,852,901 B2, 2005.

5. Mol, J. C. Industrial Applications of Olefin Metathesis. J. Molecular Catalysis A: Chemical 

2004, 213, 39–45.

6. Lavrenov, A. V.; Duplyakin, V. K. Oligomerization of Butenes on Borate-containing 

Alumina. Kinetics and Catalysis 2009, 50, 235–240.

7. Yoon, J. W.; Jhung, S. H.; Choo, D. H.; Lee, S. J.; Lee, K. Y.; Chang, J. S. Oligomerization 

of Isobutene Over Dealuminated Y Zeolite Catalysts. Applied Catalysis A: General 2008, 

337, 73–77.

8. Lee, J. S.; Yoon, J. W.; Halligudi, S. B.; Chang, J. S.; Jhung, S. H. Trimerization of 

Isobutene over WOx/ZrO2 Catalysts. Applied Catalysis A: General 2009, 366, 299–303.

9. Schmidt, L. D.; Bodke, A. Autothermal Process for the Production of Olefins. U.S.

2002/0087042 A1.

10. Panuccio, G. J.; Schmidt, L. D. Increasing Olefins by H2 and CH4 Addition to the Catalytic 

Partial Oxidation of N-octane. Applied Catalysis A: General 2006, 313, 63–73.

11. Subramanian, R.; Schmidt, L. D. Renewable Olefins from Biodiesel by Autothermal 

Reforming. Angewandte Chemie-International Edition 2005, 44, 302–305.

12. Wanat, E. C.; Suman, B.; Schmidt, L. D. Partial Oxidation of Alcohols to Produce Hydrogen 

and Chemicals in Millisecond Contact Time Reactors. Journal of Catalysis 2005, 235, 18–

27.

13. Manzer, L. E.; D’Amore, M. B.; Miller, E. S.; Knapp, J. P. Process for Making Isooctenes 

from Dry 2-butanol. U.S. Patent No.: U.S. 2008/0131948 A1.
19

14. Manzer, L. E.; D’Amore, M. B.; Miller, E. S.; Knapp, J. P. Process for Making Isooctenes 

from Aqueous 2-butanol. U.S. Patent No.: U.S. 2008/0234523 A1.

15. Manzer, L. E.; D’Amore, M. B.; Miller, E. S.; Knapp, J. P. Process for Making Butenes 

from Dry 2-butanol. U.S. Patent No.: U.S. 2008/0132730 A1.

16. Manzer, L. E.; D’Amore, M. B.; Miller, E. S.; Knapp, J. P. Process for Making Butenes 

from Aqueous 2-butanol. U.S. Patent No.: U.S. 2008/0132732 A1.

17. Behrens, D. A.; Lee, I. C.; Waits, C. M. Catalytic Combustion of Alcohols for Mircoburner 

Applications. Journal of Power Sources 2010, 195, 2008–2013.

18. Taylor, J. D.; Jenni, M. M.; Peters, M. W. Dehydration of Fermented Isobutanol for the 

Production of Renewable Chemicals and Fuels. Top. Catal. 2010, 53, 1224–1230.

19. Macho, V.; Kralik, M.; Jurecekova, E.; Hudec, J.; Jurecek, L. Dehydration of C4 Alkanols 

Conjugated with a Positional and Skeletal Isomerization of the Formed C4 Alkenes. Applied 

Catalysis A: General 2001, 214, 257–257.

20. Sarathy, S. M.; Thomson, M. J.; Togbe, C.; Dagaut, P.; Halter, F.; Mounaim-Rousselle, C. 

An Experimental and Kinetic Modeling Study of N-butanol Combustion. Combustion and 

Flame 2009, 156, 852–864. 

21. Mostafa, S.; Croy, J. R.; Heinrich, H.; Cuenya, B. R. Catalytic Decomposition of Alcohols 

Over Size-selected Pt Nanoparticles Supported on ZrO2: A study of Activity, Selectivity, and 

Stability. Applied Catalysis A: General 2009, 366, 353–362.

22. St. Clair, J. G.; Lee, I. C. Catalytic Partial Oxidation of Isobutanol for the Production of 

Hydrogen. International Journal of Hydrogen Energy (Submitted on Dec 14, 2010).
20

Supplemental Materials

Table 1. Butenes/(Total Olefins) Ratio for reactions of butanol isomers: (a) 1-butanol, (b) 2-butanol, and 

(c) isobutanol.

(a)

 Empty Blank Al2O3 Rh/Al2O3

0.1757 0.6613 0.9908 0.9823 No Olefins

0.3502 0.5236 1.000 0.9812 No Olefins

0.7189 0.5202 1.000 0.9811 No Olefins

0.9392 0.5442 0.9915 0.9827 No Olefins

1.4252 0.7159 0.9829 0.9793 No Olefins

3.5018 0.6900 0.9788 0.9778 0.7593

4.7450 0.5778 0.9753 0.9801 0.8740

6.3383 0.5771 0.9704 0.9532 0.8737

(b)

 Empty Blank Al2O3 Rh/Al2O3

0.1757 0.9643 0.9889 0.9832 No Olefins

0.3501 0.9971 0.9872 0.9841 No Olefins

0.7187 1.000 0.9900 0.9864 No Olefins

0.9390 1.000 0.9917 0.9885 No Olefins

1.4248 1.000 0.9933 0.9889 No Olefins

3.5010 1.000 0.9915 0.9987 1.000

4.7484 1.000 0.9924 0.9952 0.9884

6.3312 0.9830 0.9916 0.9937 0.9789

(c)

 Empty Blank Al2O3 Rh/Al2O3

0.1757 0.8988 0.9727 0.9680 No Olefins

0.3501 0.9179 0.9252 0.9743 No Olefins

0.7187 0.9297 0.9097 0.9803 No Olefins

0.9390 0.9305 0.9234 0.9812 No Olefins

1.4248 0.9308 0.9260 0.9823 No Olefins

3.5010 0.9263 0.9173 0.9861 0.8760

4.7464 0.9203 0.9203 0.9866 0.9347

6.3377 0.9151 0.9318 0.9850 0.9511
21

Table 2. 1-Butene/2-Butenes Ratio for reactions of butanol isomers: (a) 1-butanol, (b) 2-butanol, and 

(c) isobutanol.

(a)

 Empty Blank Al2O3 Rh/Al2O3

0.1757 5.217 1.406 2.026 No Olefins

0.3502 14.83 1.472 2.080 No Olefins

0.7189 Only 1-Butene 1.416 2.157 No Olefins

0.9392 Only 1-Butene 1.429 2.326 No Olefins

1.4252 Only 1-Butene 1.431 2.397 No Olefins

3.5018 Only 1-Butene 1.465 2.451 7.854

4.7450 Only 1-Butene 1.500 2.509 1.774

6.3383 3.989 1.518 2.599 2.167

(b)

 Empty Blank Al2O3 Rh/Al2O3

0.1757 0.6303 0.6053 0.5946 No Olefins

0.3501 0.6304 0.6002 0.5791 No Olefins

0.7187 0.6318 0.5944 0.5914 No Olefins

0.9390 0.6330 0.5927 0.5928 No Olefins

1.4248 0.6323 0.5898 0.5947 No Olefins

3.5010 0.6373 0.5931 0.5866 0.4960

4.7484 0.6388 0.5937 0.5722 0.4867

6.3312 0.6407 0.6047 0.5757 0.5082

(c)

 Empty Blank Al2O3 Rh/Al2O3

0.1757 1.798 0.9323 0.9101 No Olefins

0.3501 1.922 0.9252 0.9131 No Olefins

0.7187 1.916 0.9097 0.9053 No Olefins

0.9390 1.911 0.9234 0.9138 No Olefins

1.4248 1.879 0.9260 0.9155 No Olefins

3.5010 1.883 0.9173 0.9118 Only 1-butene

4.7464 1.929 0.9203 0.8948 0.7337

6.3377 1.125 0.9318 0.8737 0.8391
22

Table 3. Cis/Trans Ratio for reactions of butanol isomers: (a) 1-butanol, (b) 2-butanol, and (c) isobutanol.

(a)

 Empty Blank Al2O3 Rh/Al2O3

0.1757 Only trans-2-

butene 1.183 1.330 No Olefins

0.3502 Only trans-2-

butene 1.208 1.355 No Olefins

0.7189 No 2-butenes 1.192 1.366 No Olefins

0.9392 No 2-butenes 1.202 1.392 No Olefins

1.4252 No 2-butenes 1.199 1.404 No Olefins

3.5018

No 2-butenes 1.196 1.364

Only trans-2-

butene

4.7450 No 2-butenes 1.204 1.353 1.104

6.3383 Only trans-2-

butene 1.213 1.331 1.160

(b)

 Empty Blank Al2O3 Rh/Al2O3

0.1757 1.035 1.145 1.184 No Olefins

0.3501 1.034 1.143 1.207 No Olefins

0.7187 1.031 1.151 1.171 No Olefins

0.9390 1.032 1.152 1.205 No Olefins

1.4248 1.030 1.149 1.207 No Olefins

3.5010 1.026 1.154 1.241 0.8862

4.7484 1.025 1.175 1.357 1.089

6.3312 1.024 1.171 1.414 1.110

(c)

cis/trans Ratio Empty Blank Al2O3 Rh/Al2O3

0.1757 0.107 1.057 1.355 No Olefins

0.3501 No cis-2-butene 1.068 1.364 No Olefins

0.7187 No cis-2-butene 1.056 1.387 No Olefins

0.9390 No cis-2-butene 1.056 1.377 No Olefins

1.4248 No cis-2-butene 1.061 1.351 No Olefins

3.5010 No cis-2-butene 1.078 1.291 No 2-butenes

4.7464 No cis-2-butene 1.060 1.471 0.7337

6.3377 0.738 1.078 1.580 0.8391
23

Table 4. Isobutene/(Linear Butenes) Ratio for reactions of butanol isomers: (a) 1-butanol, (b) 2-butanol, 

and (c) isobutanol.

(a)

 Empty Blank Al2O3 Rh/Al2O3

0.1757 0 0 0 No Olefins

0.3502 0 0 0 No Olefins

0.7189 0 0 0 No Olefins

0.9392 0 0 0 No Olefins

1.4252 0 0 0 No Olefins

3.5018 0 0 0 0

4.7450 0 0 0 0

6.3383 0 0 0 0

(b)

 Empty Blank Al2O3 Rh/Al2O3

0.1757 0 0 0.02096 No Olefins

0.3501 0 0 0.01019 No Olefins

0.7187 0 0 0 No Olefins

0.9390 0 0 0 No Olefins

1.4248 0 0 0 No Olefins

3.5010 0 0 0 0

4.7484 0 0 0 0

6.3312 0 0 0 0

(c)

 Empty Blank Al2O3 Rh/Al2O3

0.1757 2.432 1.753 3.195 No Olefins

0.3501 2.501 1.794 3.223 No Olefins

0.7187 2.481 1.873 3.362 No Olefins

0.9390 2.504 1.920 3.394 No Olefins

1.4248 2.504 1.913 3.316 No Olefins

3.5010 2.505 1.938 3.140 18.81

4.7464 2.532 1.913 3.509 2.928

6.3377 2.060 1.921 3.866 2.953
24

List of Symbols, Abbreviations, and Acronyms

CO carbon monoxide

CO2 carbon dioxide

GC gas chromatograph

HP-INNOWAX Brand name of a separation column for gas chromatography

HPLC High Performance Liquid Chromatography

MTBE methyl tert-butyl ether

N2 nitrogen

O2 oxygen
25

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