Catalytic Performance For Propane Dehydrogenation Research Articles

Modulation of metal–support interactions in Pt–TiOx synergistic catalysts for propane dehydrogenation

The strong metal-support interaction exerts a significant influence on the catalytic performance of the metal active site. This paper describes the modulation of the coverage of TiOx on the Pt nanoparticles via the pretreatment atmosphere, and its influence of the catalytic performance for propane dehydrogenation. The direct reduction in H2 at 600 °C of the Pt/TiO2-Al2O3 catalyst induces partial coverage of the Pt nanoparticles by TiOx. This partial coverage with TiOx leads to higher electron density over platinum than catalysts treated through air calcination followed by reduction, which can enhance the selectivity of propylene. Furthermore, the presence of TiOx in the catalysts can promote C–H activation during propane dehydrogenation. Eventually, this synergistic catalyst presents a high formation rate of propylene (141.1 mmol·gcat-1·h−1) and propylene selectivity of ∼ 91 % with a low deactivation rate of 0.09 h−1. This study unveils an effective approach to modulate the catalytic performance of metals supported on oxides based on metal-support interaction.

Structure Robustness of Highly Dispersed Pt/Al2O3 Catalyst for Propane Dehydrogenation during Oxychlorination Regeneration Process

The structure and performance stability of a Pt-based catalyst for propane dehydrogenation during its reaction–regeneration cycles is one of the key factors for its commercial application. A 0.3% Pt/Al2O3 catalyst with a sub-nanometric particle size was prepared and two different types of regeneration processes, long-term dichloroethane oxychlorination and a reaction–oxidation–oxychlorination cycle, were investigated on this catalyst. The fresh, sintered and regenerated catalyst was characterized by HAADF-STEM, CO-DRIFTS, XPS, CO chemisorption and N2 physisorption, and its catalytic performance for propane dehydrogenation was also tested. The results show that the catalysts tend to have a similar particle size, coordination environment and catalytic performance with the extension of the regeneration time or an increase in the number of cycles in the two regeneration processes, and a common steady state could be achieved on the catalysts. This indicates that structure of the catalyst tends to approach its equilibrium state in the regeneration process, during which the utilization efficiency of Pt is maximized by increasing the dispersion of Pt and its intrinsic activity, and the structural robustness is secured. The performance of the catalyst is comparable to that of a single-atom Pt/Al2O3 catalyst.

Propane dehydrogenation over Pt and Ga-containing MFI zeolites with modified acidity and textural properties

A variety of oxides (titanium, tin, calcium, magnesium, and gallium) were supported over nano-crystalline ZSM-5 zeolite (n-ZSM-5) by wet impregnation, characterized and evaluated for propane dehydrogenation (PDH) reaction. To enhance the catalytic performance of the oxide-modified n-ZSM-5, Pt nanoparticles were also dispersed over the oxides-supported zeolite catalysts by wet impregnation. Finally, Ga-containing MFI zeolites were used as catalysts in the PDH. Ga was incorporated into the zeolite by two different methods, via hydrothermal synthesis and via wet impregnation. In the PDH reaction, Pt-containing samples exhibited a high initial catalytic activity although they suffered a fast deactivation by coke deposition. On the contrary, Ga-containing MFI catalysts showed a remarkable stability in the PDH reaction. In particular, the catalyst in which Ga was incorporated into the MFI structure by hydrothermal synthesis (Ga-MFI (nSH)) achieved the highest catalytic performance in PDH (9% conversion and 80% propylene selectivity) due to the synergy between the Brønsted and Lewis acid sites (BAS and LAS) and the optimal strength of its LAS sites. These results denote the great potential of Ga-MFI zeolites as catalysts in PDH reactions.

Influence of catalyst pelletization on propane dehydrogenation over hierarchical MFI zeolite supported with platinum-yttrium nanoparticles

Platinum-yttrium (PtY) nanoparticles supported on a siliceous form of mesoporous MFI zeolite (MZ) were recently found to exhibit excellent catalytic performance in propane dehydrogenation (PDH). Herein, potential shaping of the PtY/MZ catalyst is investigated from the laboratory-synthesized powder form into industrially preferable pellets. The MZ zeolite powder was synthesized using multi-ammonium surfactants as a structure-directing agent and then pelletized in a hydraulic press by itself or with inorganic binders (i.e., pseudoboehmite, fumed silica, or hydrotalcite). As a part of the sequential pelletization process, pressing was followed by a high-temperature treatment (923 K). Addition of 20 wt% pseudoboehmite resulted in the highest mechanical strength without a significant loss of the initial zeolite mesoporosity. The pseudoboehmite-bound pellet also showed high catalytic activity and longevity in PDH application when simultaneously impregnated with 1 wt% Pt [Pt(NH3)4(NO3)2] and 1 wt% Y [Y(NO3)2·6H2O]. Notwithstanding the observed high propane conversion, the pseudoboehmite-bound catalyst produced an unsatisfactory result of low propylene selectivity (∼60%). Image analyses of HAADF-STEM EDS and solid-state 31P NMR spectroscopic data suggest that such findings could be attributed to Al migration from pseudoboehmite onto zeolite regime during the phase transformation of pseudoboehmite in the shaping process. Alternatively, the uses of non-acidic binders, such as fumed silica and hydrotalcite binders were also demonstrated. The silica-bound catalyst yielded high propane conversion with high propylene selectivity although mechanical strengths of the pellet were compromised to a moderate level.

Effect of yttrium on catalytic performance of Y-doped TiO2 catalysts for propane dehydrogenation

Defective bulk catalysts based on TiO2 have superior catalytic performance for propane dehydrogenation (PDH). The oxygen vacancy concentration and the number of active sites on the catalyst surface can be effectively tuned by doping metal in TiO2. Herein, yttrium (Y)-doped titanium dioxide (nY/TiOx) catalysts were in-situ synthesized via the coprecipitation method to study the effect of rare earth metal Y doping on the structure of TiO2 and the catalytic performance for PDH. Experimental results demonstrate that Y-doped TiO2 exhibits higher catalytic activity, propylene selectivity and stability than bare TiO2. Full characterizations with X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM), X-ray photoelectron spectroscopy (XPS), infrared spectroscopy of pyridine adsorption (Py-IR), temperature-programmed desorption of ammonia (NH3-TPD), H2 temperature-programmed reduction (H2-TPR), and Raman techniques on these catalysts reveal that Y3+ can enter TiO2 lattice, and the lattice stability of the catalyst can be enhanced by replacing Ti4+ to form Y–O–Ti structure. Meanwhile, the introduction of an appropriate amount of Y can obviously promote the PDH reaction by adjusting the acidity of the catalyst, improving the release capacity of TiO2 lattice oxygen and increasing the formation of active centers. Nevertheless, excessive Y doping will lead to pore clogging, and the exposure of active sites will be reduced, resulting in the degradation of catalytic performance.

Nonoxidative propane dehydrogenation by isolated Co2+ in BEA zeolite: Dealumination-determined key steps of propane C[sbnd]H activation and propylene desorption

With BEA (Si/Al = 20) zeolite and dealuminated Si-BEA as supports, the non-noble metal Co catalysts are prepared by vacuum impregnation method to study the correlation between the catalyst structure and catalytic performance in propane dehydrogenation (PDH) reaction . The optimal 0.5 wt% Co@Si-BEA catalyst exhibits over 93 % selectivity to propylene, high single-pass yield and great regeneration stability in the recycling PDH reactions at 590 °C. The isolated Co2+ cations are anchored in the micropores of Si-BEA zeolites through interacting with the silanol groups generated by dealumination treatment, and serve as the catalytically active sites to selectively activate the CH bonds of propane rather than dissociate the CC bonds. Furthermore, Co@Si-BEA catalyst adsorbs propylene in a favorable configuration, leading to desired adsorption features with respect to less amount and weaker strength in comparison with that on non-dealuminated Co@BEA catalyst. Therefore, the facile propylene desorption can be achieved on Co@Si-BEA catalyst, which is responsible for its high propylene selectivity, activity, and long-term stability in PDH reaction. By contrast, Co@BEA catalyst with higher density of surface Brønsted acid sites, facing with severe issues of propane CC bond scission, strong propylene adsorption and coke deposition-caused deactivation.

Atomically dispersed Pt in ordered PtSnZn intermetallic with Pt−Sn and Pt−Zn pairs for selective propane dehydrogenation

With the surge of shale gas, propane dehydrogenation becomes increasingly important to synthesize propylene. Herein, a new type of ordered PtSnZn intermetallic clusters (∼0.9 nm) supported on Al2O3 was synthesized by a stepwise approach including electrostatic adsorption and temperature-programmed reduction. The structure of the PtSnZn clusters results from a kinetically controlled process, and Pt atoms in the PtSnZn clusters are well isolated by Sn and Zn with Pt−Sn and Pt−Zn pairs. The PtSnZn/Al2O3 catalyst exhibits excellent catalytic performance for propane dehydrogenation, which achieves ∼100% propylene selectivity and keeps a high propane conversion (>40%) during stability testing. The catalytic performance of PtSnZn/Al2O3 is also significantly higher than that of Pt/Al2O3, PtSn/Al2O3, and PtZn/Al2O3. Experiments and theoretical calculations indicate that the Sn 5p and Zn 4s orbitals are hybridized with Pt 5d by forming Pt−Sn and Pt−Zn pairs, which leads to the d band center of Pt deviating from Fermi level (−2.81 eV). The shift of the Pt d band center significantly decreases the adsorption energy of propylene and prohibits further dehydrogenation, resulting in high propylene selectivity and stability.

Dendritic Mesoporous Silica Nanoparticle Supported PtSn Catalysts for Propane Dehydrogenation.

PtSn catalysts were synthesized by incipient-wetness impregnation using a dendritic mesoporous silica nanoparticle support. The catalysts were characterized by XRD, N2 adsorption-desorption, TEM, XPS and Raman, and their catalytic performance for propane dehydrogenation was tested. The influences of Pt/Sn ratios were investigated. Changing the Pt/Sn ratios influences the interaction between Pt and Sn. The catalyst with a Pt/Sn ratio of 1:2 possesses the highest interaction between Pt and Sn. The best catalytic performance was obtained for the Pt1Sn2/DMSN catalyst with an initial propane conversion of 34.9%. The good catalytic performance of this catalyst is ascribed to the small nanoparticle size of PtSn and the favorable chemical state and dispersion degree of Pt and Sn species.

Mesoporous Silica SBA-15 Supported Pt–Ga Nanoalloys as an Active and Stable Catalyst for Propane Dehydrogenation

Propane dehydrogenation is one of the most admired technologies for propylene production. However, the development of an active and stable catalyst presents a significant challenge. In this study, Pt–Ga/SBA-15 catalysts were prepared via coimpregnation, followed by H2 reduction, and applied in propane dehydrogenation. The Pt–Ga/SBA-15 catalyst with a Ga/Pt molar ratio of 1 exhibited a high propane conversion of up to 60% and high selectivity toward propylene of 98.2% at 550 °C for 10 min, with a propane conversion of 51.6% and propylene selectivity of 99.5% after reaction for 25 h. The physicochemical properties characterized using N2 physisorption, XRD, TEM, XPS, CO chemisorption, and in situ CO–DRIFT spectroscopy reveal that the Pt–Ga alloy nanoparticles were formed on the SBA-15 support after direct reduction with H2. The study of coke formation via temperature-programmed oxidation showed that a large amount of coke was deposited over the support of spent Pt–Ga/SBA-15 catalyst, indicating coke mobility from the active sites to the supports and its contribution to catalyst stability. The activities of spent catalysts could be almost completely recovered via reduction regeneration, during which Pt–Ga alloy retains the original geometrical and electronic structure well. The dilution of Pt ensembles due to the addition of Ga, e.g., Pt–Ga alloy formation, plays an important role in enhancing the catalytic performance for propane dehydrogenation.

Promoting Propane Dehydrogenation with CO2 over the PtFe Bimetallic Catalyst by Eliminating the Non-selective Fe(0) Phase

Fine tuning the structure of bimetallic nanoparticles is critical toward understanding structure–activity relationships and further improving the catalytic performance in propane dehydrogenation (PDH). Excessive Fe species in the PtFe bimetallic catalysts promote carbon deposition leading to low propylene selectivity, and it remains challenging to synthesize well-defined PtFe catalysts while selectively eliminating the excessive Fe. Herein, we show that the formation of coke can be significantly inhibited by introducing CO2 into the PDH over PtFe catalysts, where CO2 effectively eliminates the active Fe(0) coking sites without changing the catalytic surface structure of the PtFe alloy. With a CO2/C3H8 feeding ratio of 0.20, the Pt1Fe7/S-1 catalyst shows the highest propylene production rate and decreased amount of coke from 18.8 to 1.0 wt % compared with dehydrogenation without CO2. X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, and 57Fe Mössbauer results indicate that it is the oxidation of excessive unalloyed Fe species during the CO2-PDH reaction, instead of the reverse Boudouard reaction (CO2 + C = 2CO), that significantly inhibits the carbon deposition. This work provides a promising strategy for tuning the structure of PtFe bimetallic catalysts under reaction conditions and improving the performance of the PDH reaction.

Propane Dehydrogenation over PtSn/Al2O3 Catalysts: Influence of Urea to Al(NO3)3·9H2O Ratio

Al2O3 supports were synthesized by the hydrothermal method and PtSn/Al2O3 catalysts were prepared by incipient-wetness impregnation method. The influence of the ratio of urea to Al(NO3)3·9H2O on the structure and catalytic performance for propane dehydrogenation was investigated. The catalysts were characterized by XRD, N2 adsorption–desorption, SEM, H2-TPR, NH3-TPD and Raman. The results show that the ratios of urea to Al(NO3)3·9H2O influence the morphology and phy-chemical properties of Al2O3 support, which influence the dispersion of PtSn active sites and the interaction of Pt and Sn on PtSn/Al2O3 catalysts. The PtSn/Al2O3-9 catalyst possesses the highest interaction of Pt and Sn, which result in high dispersion of active sites. The PtSn/Al2O3-9 catalyst shows high propane conversion and low deactivation rate among these catalysts.

A critical evaluation of the catalytic role of CO2 in propane dehydrogenation catalyzed by chromium oxide from a DFT-based microkinetic simulation.

Propane dehydrogenation under CO2 is an important catalytic route to obtain propene with a good balance between selectivity and stability. However, a precise description of the catalytic role of CO2 in propane dehydrogenation is still absent. In this work, we focus on the elucidation of the role of CO2 by using DFT-based microkinetic simulation. The influence of CO2 is categorized as direct and indirect effects. It was found that the chemisorbed CO2 can directly abstract hydrogen from propane and propyl with a comparable barrier to the counterpart at the surface oxygen site. On the other hand, the dissociation of CO2 yields active surface species of CO* and O* which are actively involved in the removal of surface hydroxyls. It is found that the TOFs of both propane conversion and propene formation are significantly increased with the presence of CO2, which is explained by the reduced apparent activation energy. The primary hydrogen abstraction is identified to be the most influential step from the DRC analysis. The main effects of CO2 are concluded to be removing hydrogen and restoring oxygen vacancies from reaction pathway analysis.

Effective synthesis of vanadium-doped mesoporous silica nanospheres by sol-gel method for propane dehydrogenation reaction

The vanadium-doped mesoporous silica nanospheres ( n V−MSNs) with worm−like porous structure were successfully synthesized by simple sol−gel method and applied to propane dehydrogenation (PDH) reaction. The moderate introduction of vanadium species didn't affect the self−assembly of the worm−like porous structure of support. The prepared samples were characterized by X-ray diffraction (XRD), Raman, X-ray photoelectron spectra (XPS), temperature–programmed desorption (TPD) of NH 3 and temperature-programmed reduction (TPR) with H 2 to investigate the influence of the chemical states of VO X on the catalytic properties in PDH reaction. It is found that the appropriate amount and high dispersion degree of VO X species of the n V−MSNs catalyst is the key to obtain excellent catalytic performance in PDH. It is shown that 9V−MSNs catalyst exhibits optimum reaction activity with an initial propane conversion of 50.6% at 600 ° C. The catalyst obtains the maximum percentage of active V V species, and has better vanadium dispersion than others, which is demonstrated by Raman and XPS analysis. 9V−MSNs catalyst also exhibits outstanding activity and stability in reaction−regeneration for six cycles. Hence, the prepared n V−MSNs catalysts hold immense potential to further development in application of PDH. • Vanadium-doped mesoporous silica nanospheres ( n V-MSNs) were synthesized. • n V-MSNs show superior TOF value for propane dehydrogenation reaction. • Vanadium content influences its chemical states and polymerization degree. • The deactivated catalyst can be fully recovered after regeneration.

Propane dehydrogenation over core–shell structured Al2O3@Al via hydrothermal oxidation synthesis

A novel dehydrogenation catalyst, core–shell structured Al2O3@Al via hydrothermal oxidation synthesis, demonstrates good catalytic performance for propane dehydrogenation. According to the characterization results, the hydration of metallic Al powder results in the appearance of nanosheet-like AlOOH and Al(OH)3 species on the surface, which are regarded as the precursor of the active sites responsible for propane dehydrogenation. Compared with traditional γ-Al2O3 sample, the novel Al2O3@Al catalyst with more coordinatively unsaturated Al3+ leads to enhanced formation rate of propene and shortened induction period, which can be attributed to the high density of corner and edge sites on the surface of lamella-like AlOOH and/or Al(OH)3 species. More importantly, a significantly increased selectivity to propene can also be achieved, especially by introducing Na.

Sodium-free synthesis of mesoporous zeolite to support Pt-Y alloy nanoparticles exhibiting high catalytic performance in propane dehydrogenation

Mesoporous zeolite-supported Pt3Y catalyst deactivates slowly in propane dehydrogenation, maintaining high propane conversion and propylene selectivity, but the formation of the intermetallic compound requires atomistic migration of yttrium through silanol nests on the zeolite. Compared to the cumbersome generation of silanols via framework demetallation, we report a direct synthesis of mesoporous MFI zeolite possessing silanol nests. The synthesis procedure employed a diammonium-type bromide surfactant [C18H37N(CH3)2C6H12N(CH3)2C4H9Br2] and a sodium-free silica source. The basicity of the synthesis mixture was adjusted by the addition of readily available N(CH3)4OH, instead of converting the surfactant to hydroxyl form. The presence of silanol nests in the resultant zeolite was confirmed by IR and NMR spectroscopies. When the zeolite was supported with 0.50 wt% Pt and 0.50 wt% Y using nitrate precursors, a remarkably long catalytic lifetime of 20 days was obtained with high propane conversion and propylene selectivity under the reaction condition using neat propane gas at 853 K.

Correlating the Structural Evolution of ZnO/Al2O3 to Spinel Zinc Aluminate with its Catalytic Performance in Propane Dehydrogenation

Zn-based Al2O3-suported materials have been proposed as inexpensive and environmentally friendly catalysts for the direct dehydrogenation of propane (PDH), however, our understanding of these catalysts’ structure and deactivation routes is still limited. Here, we correlate the catalytic activity for PDH of a series of Zn-based Al2O3 catalysts with their structure and structural evolution. To this end, three model catalysts are investigated. (i) ZnO/Al2O3 prepared by atomic layer deposition (ALD) of ZnO onto γ-Al2O3 followed by calcination at 700 °C, which yields a core-shell spinel zinc aluminate/γ-Al2O3 structure. (ii) Zinc aluminate spinel nanoparticles (ZnxAlyO4 NPs) prepared via a hydrothermal method. (iii) A reference core-shell ZnO/SiO2 catalyst prepared by ALD of ZnO on SiO2. The catalysts are characterized in detail by synchrotron X-ray powder diffraction (XRD), Zn K-edge X-ray absorption spectroscopy (XAS), and 27Al solid state nuclear magnetic resonance (ssNMR). These experiments allowed us to identify tetrahedral Zn sites in close proximity to Al sites of a zinc aluminate spinel phase (ZnIV–O–AlIV/VI linkages) as notably more active and selective in PDH relative to the supported ZnO wurtzite phase (ZnIV–O– ZnIV linkages) in ZnO/SiO2. The best performing catalyst, 50ZnO/Al2O3 gives 77% selectivity to propene (gaseous products based) at 9 mmol C3H6 gcat−1 h−1 space time yield (STY) after 3 min of reaction at 600 °C. On the other hand, the core-shell ZnO/Al2O3 catalyst shows an irreversible loss of activity over repeated PDH and air-regeneration cycles, explained by Zn depletion on the surface due to its diffusion into subsurface layers or the bulk. ZnxAlyO4 NPs gave a comparable initial selectivity and catalytic activity as 50ZnO/Al2O3. With time on stream, ZnxAlyO4 NPs deactivate due to the formation of coke at the catalyst surface, yet the extend of coke deposition is lower than for the ZnO/Al2O3 catalysts, and the activity of ZnxAlyO4 NPs can be regenerated almost fully using calcination in air.

Spatially isolated cobalt oxide sites derived from MOFs for direct propane dehydrogenation

The “active site isolation” strategy has been proved to be efficient for enhancing the catalytic performance in propane dehydrogenation (PDH). Herein, spatially isolated cobalt oxide sites within nitrogen-doped carbon (NC) layers supported on silicalite-1 zeolite (CoOx@NC/S-1) were synthesized by a two-step process consisting of the pyrolysis of bimetallic Zn/Co zeolitic imidazole frameworks loaded on silicalite-1 (ZnCo-ZIF/S-1) under N2 and the subsequent calcination in air atmosphere. This catalyst possesses exceptional catalytic performance for PDH with the propane conversion of 40% and the propene selectivity of >97%, and no apparent deactivation is observed after 10 h PDH reaction at 600 °C. With intensive characterizations and experiments, it is indicated that the real active sites of CoOx@NC/S-1 are isolated CoO sites during the PDH process. In situ FT-IR spectroscopy shows the same intermediate product (Co-C3H7) during both propane dehydrogenation and propene hydrogenation, indicating that they have a reverse reaction process, and a reaction mechanism for PDH is proposed accordingly.

Non-oxidative propane dehydrogenation over alumina-supported Co-V oxide catalysts

CoOx-based catalysts have been suggested as promising catalysts for C–H bond activation and C–C bond formation. For supported CoOx catalysts, surface concentration, reducibility, and oxidation state of Co species are important properties determining the catalytic performance. Herein, we prepare alumina-supported Co-V oxide catalysts to enhance the catalytic performance for propane dehydrogenation (PDH). The change in the properties of Co oxides by V component and the effect on the performance are investigated by in-situ XAS and ex-situ characterizations. The presence of the V component improves the reducibility of Co nanoparticles by modifying the interactions of Co with Al2O3. The catalytic performance results, combined with the characterizations, show that the increase in the surface concentration of metallic Co species by V component leads to the enhanced performance of alumina-supported Co-V oxide catalysts for PDH.

Mn-doping induced changes in Pt dispersion and PtxMny alloying extent on Pt/Mn-DMSN catalyst with enhanced propane dehydrogenation stability

The development of highly stable propane dehydrogenation catalyst is significant with the growing extraction of shale gas in the world. A highly dispersed MnOx site decorated dendritic mesoporous silica nanoparticle support was prepared by simple in-situ emulsion method. It shows exceptionally ability to disperse and stabilize Pt clusters. The strong interaction between Pt and Mn formed and the electron transfer happened from Mn to Pt, which leads to an increase in the electron density of Pt. The high propane dehydrogenation activity, even for 100 h long-term test, was obtained on moderate Mn content catalyst. According to the experimental results and DFT calculation, the highly dispersed PtMn alloyed nanoparticles play an important role in enhancing the catalytic performance for propane dehydrogenation via a good balance on propane activation and propene desorption.

Ultrasmall PtZn bimetallic nanoclusters encapsulated in silicalite-1 zeolite with superior performance for propane dehydrogenation

Bimetallic catalysts have attracted increasing attention in propane dehydrogenation (PDH) due to the synergistic effect of metal species and considerably improved catalytic performance, but they often suffer from severe sintering and poor stability. Here, well-dispersed and ultrasmall PtZn bimetallic nanoclusters encapsulated in silicalite-1 (S-1) zeolites (named PtZn@S-1) are prepared via a facile in situ synthesis strategy. It is indicated that the PtZn bimetallic nanoclusters with ultrasmall size are homogeneously dispersed within the channels of S-1 zeolites. The 0.3Pt0.5Zn@S-1 catalyst shows excellent catalytic performance in PDH with a propane conversion of 45.3% and a propylene selectivity of >99%, and no visible sintering of PtZn bimetallic nanoclusters is observed in the long-term PDH reaction at 550 °C. The excellent catalytic properties and high stability of the ultrasmall bimetallic nanoclusters confined in zeolites create new prospects for PDH.