Highly Effective Oxidative Dehydrogenation of Propane Over Vanadia Supported on Mesoporous SBA-15 Silica

Vanadia-containing mesoporous SBA-15 catalysts were prepared and characterized for the oxidative dehydrogenation (ODH) of propane. It is demonstrated that the vanadia-supported SBA-15 catalysts exhibit a much higher catalytic activity than those reported in the literature obtained over vanadium-supported mesoporous MCM-41 catalysts in the ODH of propane. The high catalytic performance of the mesoporous SBA-15 catalysts is attributed to the particularly large pore diameters and low surface acidity.     

Dehydrogenation of Propane on Pt or PtSn Catalysts with Al2O3 or SBA-15 Support

Dehydrogenation of propane on Pt or PtSn catalyst over Al2O3 or SBA-15 support was investigated. The catalysts were characterized by CO-pulse chemisorption, thermogravimetry, temperature-programmed-red...     

Dehydrogenation of Propane in the Presence and Absence of CO2 Over β-Ga2O3 Supported Chromium Oxide Catalysts

The dehydrogenation of propane to propene in the presence and absence of CO₂ over β-Ga₂O₃ supported chromium oxide catalysts has been studied. The effect of chromium content and feed composition on the dehydrogenation of propane has been investigated. It has been found that deposition of chromium oxide enhances the dehydrogenation activity and resistance to coke deposition. Moreover, it has been shown that CO₂ promotes the dehydrogenation of propane above 848 K. At that temperature in the presence of CO₂ both the yield of propene and conversion of propane were higher than in the inert gas atmosphere.     

丙烷氧化脱氢负载型催化剂的研究

制备了V2O5/TiO2和V2O5/TiO2 ZrO2负载型催化剂,并对催化剂进行了反应评价和BET、XRD、H2-TPR表征。通过研究验证了利用溶胶凝胶技术制备的负载TiO2催化剂有较好的低温反应活性,在250℃下反应得到2 2%的丙烯收率。对TiO2进行离子掺杂后催化剂活性组分能够和混合氧化物载体进行键合,形成稳定的O—V—Zr键和O—V—Ti键,使催化剂的还原温度从480℃增加到650℃,在350℃下反应得到12%的丙烷转化率和55%的丙烯选择性。     

Tunability of Propane Conversion over Alumina Supported Pt and Rh Catalysts

Propane conversion over alumina supported Pt and Rh (1 wt% metals loading) was examined under fuel rich conditions (C₃H₈:O₂:He = 1:2.25:9) over the temperature range 450–650 °C. Morphological characteristics of the catalyst materials were varied by calcining at selected temperatures between 500 and 1,200 °C. X-ray diffraction and BET analysis showed the treatment generated catalyts metals with particle sizes in the range of <10 to >500 nm, and support surface areas in the range of 20–240 m²/g. Remarkably, both Rh and Pt yielded product compositions close to equilibrium values (with high H₂ and CO selectivity, complete oxygen conversion and almost complete propane conversion) so long as the metal particle size was sufficiently low, ≲10–15 nm. In cases where the particle size was large, primarily complete oxidation rather than partial oxidation products were observed, along with unreacted C₃H₈, indicative of a direct oxidation pathway in which gas-phase CO and H₂ are not present as intermediate species. It is proposed that the high resistance of Rh to coarsening is largely responsible for the observation of a higher selectivity of this material for syngas products when prepared by procedures similar to those for Pt. Overall, the tunability of the product composition obtained over Rh and Pt via processing steps has direct significance for the incorporation of such catalyts into the anodes of solid oxide fuel cells.     

Oxidative dehydrogenation of n-butane over mesoporous VO x /SBA-15 catalysts

Mesoporous VO _x /SBA-15 catalysts with different V contents were evaluated for the oxidative dehydrogenation of n-butane and characterized by N₂ adsorption, XRD, HRTEM, H₂-TPR, NH₃-TPD, XPS, and EPR techniques. Compared to conventional V₂O₅/SiO₂ catalysts, the VO _x /SBA-15 catalysts showed better performance. The good performance can be attributed to the good dispersion of V species, presence of V⁴⁺ species and the pore structure.     

The Sulfur and Water Resistance of Modified Washcoated Zeolite-Exchanged Monolith Catalysts for SCR of NOx with Propane

The method of preparation of modified Cu-substituted zeolite DeNOx catalysts washcoated on monolith ceramics has been developed. Non-modified and modified monolith catalysts were tested in DeNOx reaction with propane. It was shown that the catalyst modified by cerium and containing titania together with H-ZSM-5 and Al₂O₃ in the washcoating layer demonstrates high level of activity, and its resistance during multiple cycles of poisoning by sulfur compounds and water at 400 and 500°C is also high.     

Effect of Modifiers on the Reactivity of Cr2O3/Al2O3 and Cr2O3/TiO2 Catalysts for the Oxidative Dehydrogenation of Propane

Chromium oxide supported on alumina and titania supports was modified with oxides of sodium, vanadium and molybdenum. The modified and unmodified chromium oxide catalysts were characterized by several techniques. The presence of surface chromium oxide and surface molybdenum and vanadium oxide species was detected in the unmodified and molybdenum and vanadium oxide modified supported chromium oxide catalysts. The reducibility (T_max and H/Cr ratio) of the surface chromium species was not affected for the vanadium and molybdenum oxide modified catalysts; however, the reducibility changed noticeably for sodium modified supported chromium oxide catalysts. Studies of the reactivity of the ODH of propane revealed the effect of modifiers on the reactivity properties of the surface chromium oxide species. The activity and propene selectivity decreased for sodium modified supported chromium oxide catalysts. However, the activity increased for vanadium oxide modified catalysts and was similar for molybdenum oxide modified catalysts irrespective of the support. The propene selectivity was higher for molybdenum oxide modified chromium oxide catalysts. However, the propene selectivity for vanadium oxide modified catalysts depends on the support since it appears that the inherent selectivity of the surface vanadium oxide species is reflected.     

SBA-15 as Support for MoS2 and Co-MoS2 Catalysts Derived from Thiomolybdate Complexes in the Reaction of HDS of DBT

Molybdenum sulfide and cobalt-molybdenum sulfide catalysts supported on mesoporous SBA-15 were prepared by thermal decomposition of ammonium thiomolybdate (ATM). SBA-15 was synthesized at 353 K and 413 K to obtain pore diameters of about 6 and 9 nm, respectively. The (Co)-MoS₂/SBA-15 catalysts were characterized with X-ray diffraction (XRD), N₂-physisorption and high-resolution transmission electron microscopy (HRTEM). HRTEM images give evidence for the presence of a poorly dispersed MoS₂ phase with long MoS₂ slabs and a pronounced MoS₂ stacking. The catalytic performance in the hydrodesulfurization (HDS) reaction of dibenzothiophene (DBT) was examined at T = 623 K and P = 3.4 MPa. The Co-MoS₂/SBA-15 materials show a relatively high catalytic activity with a strong preference for the direct desulfurization (DDS) pathway. This is an interesting result in view of the significant stacking of MoS₂ particles and the size of the slabs. The generation of the catalytically active CoMoS phase and a large number of coordinately unsaturated sites (CUS) may explain the high performance of Co promoted MoS₂/SBA-15 catalysts in the HDS reaction. A confinement effect of the mesoporous channels of SBA-15 is observed for the unpromoted MoS₂/SBA-15 catalysts. SBA-15 with 9 nm channel diameter with 11 wt.% Mo loading shows a higher selectivity for the hydrogenation pathway than SBA-15 with 6 nm channel and 16 wt.% Mo loading.     

Metal oxides nanoparticles on SBA-15: Efficient catalyst for methane combustion

Catalysts based on crystalline nanoparticles of Mn and Co metal oxides supported on mesoporous silica SBA-15 have been developed. These materials were characterized by XRD, BET and transmission electron microscopy (TEM) techniques. SBA-15 mesoporous silica was synthesized by a conventional sol–gel method using a tri-block copolymer as surfactant. Supported Mn₃O₄ and Co₃O₄ nanoparticles were obtained after calcination of as-impregnated SBA-15 by a metal salt precursor. The catalytic activity was evaluated in the combustion of methane at low concentration.Co₃O₄/SBA-15 (7 wt.%) exhibits the highest performance among the different oxides. Furthermore, this novel generation of catalysts appeared as active as conventional LaCoO₃ perovskite, usually taken as reference for this reaction. Thanks to its organized meso-structures, SBA-15 material creates peculiar diffusion conditions for reactants and/or products.     

Enhanced Stability of HZSM-5 Supported Ga2O3 Catalyst in Propane Dehydrogenation by Dealumination

Gallium oxide catalysts supported on HZSM-5 with different Si/Al ratios were characterized by pyridine adsorption FT-IR, model reactions and XPS studies. As the Si/Al ratio of the support HZSM-5 zeolite rises, the acidity of the supported catalysts decreases accordingly, which comes from two aspects: the loss of acid sites present on HZSM-5 support and the loss of the acid sites present on gallium oxides. The latter was caused by the change in the interaction between Ga₂O₃ and support. The initial activity in the propane dehydrogenation decreases with increasing Si/Al ratio while the stability increases. The enhanced stability is thought to be caused by the decrease of the acidity of the catalysts, resulting in the suppression of the side reactions, such as cracking and oligomerization.     

Oxidative Conversion of Propane over Al2O3-Supported Molybdenum and Chromium Oxides

Oxidative dehydrogenation of propane has been studied on Mo/-Al₂O₃ catalysts with 13 wt% of MoO₃ and promoted with Cr. The catalysts were characterized by BET, X-ray diffraction, XPS, TPR, TPO and isopropanol decomposition. The ODH results indicated an important increase in propane conversion with Cr loading increase from 0 to 5 wt%. At 773 K the conversion increased 1.5 times whereas the selectivity to propene was not significantly modified. The higher activities obtained on Cr-doped catalysts provide for the technologically important possibility of carrying out the reaction at lower temperatures.     

Activation of Supported Pd Metal Catalysts for Selective Oxidation of Hydrogen to Hydrogen Peroxide

Catalytic activity of supported Pd metal catalysts (Pd metal deposited on carbon, alumina, gallia, ceria or thoria) showing almost no activity in the liquid-phase direct oxidation of H₂ to H₂O₂ (at 295 K) in acidic medium (0.02 M H₂SO₄) can be increased drastically by oxidizing them using different oxidizing agents, such as perchloric acid, H₂O₂, N₂O and air. In the case of the Pd/carbon (or alumina) catalyst, perchloric acid was found to be the most effective oxidizing agent. The order of the H₂-to-H₂O₂ conversion activity for the perchloric-acid-oxidized Pd/carbon (or alumina) and air-oxidized other metal oxide supported Pd catalysts is as follows: Pd/alumina < Pd/carbon < Pd/CeO₂ < Pd/ThO₂ < Pd/Ga₂O₃. The H₂ oxidation involves lattice oxygen from the oxidized catalysts. The catalyst activation results mostly from the oxidation of Pd metal from the catalyst producing bulk or sub-surface PdO. It also caused a drastic reduction in the H₂O₂ decomposition activity of the catalysts. There exists a close relationship between the H₂-to-H₂O₂ conversion activity and/or H₂O₂ selectivity in the oxidation process and the H₂O₂ decomposition activity of the catalysts; the higher the H₂O₂ decomposition activity, the lower the H₂-to-H₂O₂ conversion activity and/or H₂O₂ selectivity.     

Dehydrogenation of Ethylbenzene to Styrene in the Presence of CO2 over Calcined Hydrotalcite-Like Compounds as Catalysts

Calcined hydrotalcite-like compounds were effective catalysts for the dehydrogenation of ethylbenzene in the presence of CO₂ as an oxidant. X-ray diffraction patterns suggested that the catalyst components are distributed uniformly. The activity (areal rate) of Fe(1)/Al(2)/Zn(6) oxide catalyst (molar ratios in parentheses) was the highest among the catalysts tested.     

Carbon dioxide capture under postcombustion conditions using amine-functionalized SBA-15: Kinetics and multicyclic performance

ABSTRACT

In this work, ordered mesoporous SBA-15 was synthesized and functionalized by polyethyleneimine (PEI). The morphological properties were characterized by N₂ adsorption/desorption, field–emission scanning electron microscopy (FE-SEM), high–resolution transmission electron microscopy (HR-TEM) and Fourier transform infrared (FTIR) spectroscopy methods. The carbon dioxide (CO₂) uptake on the sorbents, kinetics of CO₂ adsorption/desorption and long-term multicycle stability of PEI-impregnated sorbent were measured. An optimal amine loading of 50 wt.% showed a CO₂ adsorption capacity ~3.09 mmol g^?1 using 10% pre-humidified CO₂ at 75°C. The presence of moisture in flue gas showed a promoting effect in CO₂ sorption capacity. The temperature swing adsorption/desorption cycles showed excellent multicycle stability over 60 cycles during 65 h of operations under humid CO₂.     

Synthesis of ethanol from syngas over iron-promoted Rh immobilized on modified SBA-15 molecular sieve: Effect of iron loading

Employing modified SBA-15 molecular sieve as the support, iron-promoted Rh catalysts were investigated in the synthesis of ethanol from syngas through temperature programmed surface reaction (TPSR). Addition of promoter in certain range could partially block the rhodium surface, thereby diminishing the number of active sites and resulting in the decrease in CO conversion. However, there is not a continuous decrease in the number of active sites responsible for methane production. There exists an optimum promoter loading at which the ability of rhodium to dissociate the CO molecules is the maximum, i.e., Fe/Rh (weight ratio) = 0.5.     

Nanocrystalline CeO2 in SBA-15: Performance of Pt/CeO2/SBA-15 Catalyst for Water-gas-shift Reaction

CeO₂ particles confined within the pores of an SBA-15 mesoporous silica host were prepared by incipient wetness impregnation (IMP) and deposition precipitation (DP) methods. The materials were characterized by XRD, N₂-adsorption and temperature programmed reduction (TPR) to evaluate the structure, texture, and redox properties. The preparation procedure had significant impact on the assembling mode of CeO₂ inside the SBA-15 mesopores. A high dispersion of CeO₂ particles was achieved via DP, whereas the dispersion of CeO₂ prepared by IMP was found to be inhomogeneous and CeO₂ partially blocked the pores. The CO conversion in the water-gas-shift reaction was enhanced over 1 wt% Pt supported on CeO₂-modified SBA-15 obtained by DP.     

Deactivation of Supported Copper Catalysts for Methanol Synthesis

Binary Cu/ZnO and Cu/Al₂O₃ as well as ternary Cu/ZnO/Al₂O₃ catalysts were investigated with respect to their catalytic activity and stability in methanol synthesis. In a rapid aging test, activity measurements were carried out in combination with the determination of the specific Cu surface area. A close correlation between the loss of catalytic activity and the decrease in specific Cu surface area was found due to sintering of the Cu particles. Differences in the deactivation behavior and the area-activity relationship of each catalyst system imply that the catalysts should be grouped in different classes.     

Evaluating the Catalytic Performances of SAPO-34 Catalysts for the Oxidative Dehydrogenation of Ethane

Acid silicoaluminophosphate SAPO-34 catalysts with a chabasite-related (CHA) structure were tested for the oxidative dehydrogenation of ethane in the temperature range 550-700 °C achieving very interesting catalytic performances (about 70% C₂H₄ selectivity at 45% ethane conversion) which were related to both Lewis and Brønsted acid sites, as found by a NH₃-TPD study.     

Mechanistic Insight in the Ethane Dehydrogenation Reaction over Cr/Al2O3 Catalysts

A Cr/Al₂O₃ alkane dehydrogenation catalyst exhibits a maximum in ethylene yield during an ethane dehydrogenation cycle. Isotopic labelling experiments with monolabelled ¹³C-ethane and deuterium were used to elucidate whether the initial activity increase could be due to formation of an active, larger hydrocarbon intermediate on the surface. The results strongly indicate that this is not the case, and instead point to a traditional reaction cycle involving adsorption of ethane to form an ethyl species, followed by desorption of ethene and hydrogen. Transient kinetic data suggest that ethane adsorption is the rate-determining step of reaction.