Patent ID: 12194440

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The present invention is described in further detail by specific embodiments which enables those skilled in this field to fully understand the invention without limiting it in any way.

Embodiment 1

(1) 0.15 parts by mass of Ni(NO3)3·6H2O and 0.45 parts by mass of Zn(NO3)2·6H2O were dissolved in 1 mL of deionized water;(2) 1 part by mass of Al2O3was impregnated in the solution described above, the obtained system was subject to ultrasonic treatment for 0.5-1 h and naturally dried at room temperature for 12 h, and then completely dried at 80-100° C.;(3) the solid obtained in step (2) was calcinated in air atmosphere at 600° C. for 3 h, and then it was reduced at 600° C. for 1 h to obtain the NiZn@ZnO core-shell structured catalyst supported on Al2O3, which contained 3% of Ni based on the mass of the support, named as Ni1Zn3/Al2O3;(4) the prepared catalyst was ground and sieved to a certain size (20-40 mesh); and(5) the prepared catalyst was loaded into a fixed-bed reactor, and the reaction was operated under a mixture of C3H6and H2(molar ratio: 1:1) within N2as a balance gas. The weight hourly space velocity (WHSV) of propane was 4 h−1.

Embodiment 2

This embodiment was carried out using the method described in Embodiment 1 for preparation and reaction with 0.45 parts by mass of Zn(NO3)2·6H2O in step (1) being replaced by 0.15 parts by mass; and the catalyst contained 3% of Ni based on the mass of the support, named as Ni1Zn1/Al2O3.

Embodiment 3

This embodiment was carried out using the method described in Embodiment 1 for preparation and reaction with 0.45 parts by mass of Zn(NO3)2·6H2O in step (1) being replaced by 0.6 parts by mass; and the catalyst contained 3% of Ni based on the mass of the support, named as Ni1Zn4/Al2O3.

Embodiment 4

This embodiment was carried out using the method described in Embodiment 1 for preparation and reaction with 0.45 parts by mass of Zn(NO3)2·6H2O in step (1) being replaced by 0.05 parts by mass; and the catalyst contained 3% of Ni based on the mass of the support, named as Ni3Zn1/Al2O3.

Embodiment 5

This embodiment was carried out using the method described in Embodiment 1 for preparation and reaction with 0.45 parts by mass of Zn(NO3)2·6H2O in step (1) being replaced by 0 parts by mass; and the catalyst contained 3% of Ni based on the mass of the support, named as Ni/Al2O3.

Embodiment 6

This embodiment was carried out using the method described in Embodiment 1 for preparation and reaction with 0.15 parts by mass of Ni(NO3)3·6H2O in step (1) being replaced by 0 parts by mass, and the catalyst contained 10% of Zn based on the mass of the support, named as ZnO/Al2O3.

Embodiment 7

This embodiment was carried out using the method described in Embodiment 1 for preparation and reaction with 0.15 parts by mass of Ni(NO3)3·6H2O in step (1) being replaced by 0.025 parts by mass, and the catalyst contained 0.5% of Ni based on the mass of the support, named as Ni1Zn3/Al2O3.

Embodiment 8

This embodiment was carried out using the method described in Embodiment 1 for preparation and reaction with 0.15 parts by mass of Ni(NO3)3·6H2O in step (1) being replaced by 0.05 parts by mass, and the catalyst contained 1% of Ni based on the mass of the support, named as Ni1Zn3/Al2O3.

Embodiment 9

This embodiment was carried out using the method described in Embodiment 1 for preparation and reaction with 0.15 parts by mass of Ni(NO3)3·6H2O in step (1) being replaced by 0.3 parts by mass, and the catalyst contained 6% of Ni based on the mass of the support, named as Ni1Zn3/Al2O3.

Embodiment 10

This embodiment was carried out using the method described in Embodiment 1 for preparation and reaction, and only differed in that in step (3), the calcination temperature was 400° C.

Embodiment 11

This embodiment was carried out using the method described in Embodiment 1 for preparation and reaction, and only differed in that in step (3), the calcination temperature was 500° C.

Embodiment 12

This embodiment was carried out using the method described in Embodiment 1 for preparation and reaction, and only differed in that in step (3), the calcination time was 2 h.

Embodiment 13

This embodiment was carried out using the method described in Embodiment 1 for preparation and reaction, and only differed in that in step (3), the calcination time was 4 h.

Embodiment 14

This embodiment was carried out using the method described in Embodiment 1 for preparation and reaction, and only differed in that in step (3), the reduction temperature was 500° C.

Embodiment 15

This embodiment was carried out using the method described in Embodiment 1 for preparation and reaction, and only differed in that in step (3), the reduction temperature was 700° C.

Embodiment 16

This embodiment was carried out using the method described in Embodiment 1 for preparation and reaction, and only differed in that in step (3), the reduction time was 2 h.

The catalysts prepared in the above embodiments were tested for catalytic performance in the propane dehydrogenation reaction, and the catalyst activity was expressed in terms of conversion of propane, selectivity of propylene, and deactivation rate, which will be discussed below in combination with the calculation results:

The catalysts of Embodiments 1 to 6 corresponding to different Ni/Zn ratios were tested for catalytic performance in propane dehydrogenation, and their catalytic performances were shown inFIG.1, where (a), and (b) show the conversion of C3H6and selectivity of C3H6as a function of time on stream over various NixZny/Al2O3, respectively, and (c) shows the comparison of deactivation rate constant over different catalysts. As can be seen fromFIG.1, the NixZny/Al2O3catalysts corresponding to Embodiments 1 to 3 performed well in catalytic stability; whereas pure Ni/Al2O3of Embodiment 5 showed high initial activity, but poor selectivity to propylene and underwent an induction period during which rapid deactivation occurred due to the fast coke deposition covering the highly reactive sites, thereafter becoming relatively stable and low-active. The ZnO/Al2O3of Embodiment 6 exhibited consistent high selectivity towards propylene but low activity with a propensity for continuous rapid deactivation with a deactivation rate constant (kd) higher than 0.37 h−1, indicating a poor stability during the propane dehydrogenation reaction. In addition, as can be seen fromFIG.1, with the increase of Zn addition, the catalytic behavior of NixZny/Al2O3tended to transform from Ni-like to ZnO-like which may imply the transformation of active sites. For Ni1Zn3/Al2O3, the deactivation tendency was significantly suppressed and higher activity together with similar selectivity was achieved when compared with ZnO/Al2O3, with an initial conversion of propane of 37%, and a selectivity of propene of more than 90%.

Embodiments 1, 7, 8 and 9 provide catalysts prepared with different Ni loadings (based on the mass of the support) and their catalytic performance in propane dehydrogenation. It can be seen fromFIG.2that the conversion of propane increased gradually with the increase of Ni loading. But the selectivity to propylene dropped dramatically as the Ni loading increased to 6 wt %, which can be attributed to the partial exposure of Ni sites resulting from the higher Ni content. The catalytic performance was optimal when the content of Ni was 3 wt %.

Embodiments 1, 14 and 15 provide catalysts prepared at different reduction temperatures and their catalytic performance in propane dehydrogenation. It can be seen fromFIG.3that there was no significant change in the catalytic performance when the reduction temperature was between 500° C. and 600° C., but the conversion of propane decreased significantly when the reduction temperature was increased to 700° C., which can be explained by the deep reduction of ZnO as an active species, forming metallic Zn with a lower melting point (420° C.) and no activity for propane dehydrogenation, resulting in the decrease in activity.

The catalyst prepared in Embodiment 1 was further subject to a long-term regeneration stability test at 550° C., and the result is shown inFIG.4. While maintaining a stable selectivity of more than 90%, the deactivation rate constant (kd) of the Ni1Zn3/Al2O3catalyst was as low as 0.017 h−1, indicating excellent long-term stability, breaking the limitation of rapid deactivation of ZnO-based catalysts.

XRD analysis was performed over the catalysts of Embodiments 1, 2, 4 and 5 with different Ni/Zn ratios, and the resulting patterns are shown inFIG.5, where I, II, III and IV correspond to Embodiments 5, 4, 2 and 1, respectively. the transformation trend from Ni(111) to NiZn (101) can be clearly observed with the increase of Zn addition, indicating Zn incorporating into the bulk phase of Ni and the formation of NiZn alloy.

EDS-mapping analysis was performed over the Ni1Zn3/Al2O3catalyst prepared in Embodiment 1, and the images are shown inFIG.6. The uniform Ni—Zn element distribution over Al2O3support excluded the possibility of phase separation, implying the surface segregation of certain form of Zn species during the formation of NiZn alloy nanoparticles.

Also referring toFIG.7, the Ni1Zn3/Al2O3catalyst prepared in Embodiment 1 was analyzed by high-resolution TEM. The existence of homogenous ZnO overlayers on the surface of bulk NiZn alloy nanoparticles was discovered through the identification of lattice fringes, establishing a NiZn@ZnO core-shell nanostructure.

Surface-sensitive DRIFTS measurements using CO adsorption as a probe were performed on the catalysts prepared in Embodiments 1, 5 and 6, and the results are shown inFIG.8, where (a), (b) and (c) correspond to the catalysts prepared in Embodiments 5, 1 and 6, respectively. It was found that the CO adsorption peak on Ni at 2055 cm−1disappeared over Ni1Zn3, while a CO linear adsorption peak on ZnO appeared at 2198 cm−1, together with adsorption peaks of some carbonate species on ZnO at 1696 and 1522 cm−1, validating the reverse encapsulation of ZnO on Ni induced by strong metal-oxide interaction.

Furthermore, H2pulse chemisorption experiments were performed over the catalysts prepared in Embodiments 1, 2, 4 and 5 to measure the active metallic Ni surface area H2pulse chemisorption experiments were performed over the catalysts prepared in Embodiments 1, 2, 4 and 5 to measure the active metallic Ni surface area, as shown inFIG.9, where (a) displays the metallic surface area of Ni; and (b) displays conversion of propane as a function of the metallic surface area of Ni. The active metallic Ni surface area firstly increased and then gradually decreased to near zero with the increase of Zn addition. The increase could be due to the initial formation of NiZn alloy, which improved the dispersion of Ni. However, further addition of Zn gave rise to ZnO overlayers forming on the surface of NiZn alloy, leading to the reduction of metallic surface area of Ni. The near zero value of metallic Ni surface area for Ni1Zn3/Al2O3and the simultaneous reaching of the highest propane conversion confirmed the successful construction of the NiZn@ZnO core-shell structure without Ni exposure on the surface. This result excluded the assumption of Ni sites directly participating in the reaction, which meant Ni exclusively acted as a promoter while ZnO overlayers functioned as the active sites for propane dehydrogenation.

H2-TPD tests were performed on the catalysts prepared in Embodiments 1 and 6, and the results are shown inFIG.10, where (a) and (b) correspond to the catalysts prepared in Embodiments 6 and 1, respectively. These results can explain the inhibited deactivation of the ZnO species over NiZn@ZnO. The core-shell structure induced by strong metal-oxide interaction changes the geometric environment of Zn and O sites and concomitant electron transfer from the ZnO shell to the alloy core reduces the electron density of O sites, which weakens O—H binding and thus facilitates the dissociation of O—H bond in preference to dissociation of Zn—OH bond over surface ZnO, accelerating H2desorption and therefore retarding the reduction of ZnO during reaction.

Although the preferred embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to the embodiments described above, which are intended to be illustrative and not restrictive, enlightened by the present invention, those skilled in this field can make many specific changes without departing from the purpose of the present invention and the protection scope of the claims, and these all fall within the protection scope of the present invention.