Propane transformation over H-ZSM5 zeolite modified with germanium

The propane aromatization was studied over H-ZSM5 zeolite modified by Ge, Pt and Pt-Ge. The aromatization was performed in a micro-reactor at 773K and at atmospheric pressure. The addition of germanium on H-ZSM5 increases the activity for propane transformation but decreases the selectivity toward aromatic compounds. The transformation of propane on Pt/H-ZSM5 indicates a significant increase in the activity and a decrease in the selectivity toward aromatics, while on the bimetallic Pt-Ge/H-ZSM5 catalyst both the activity and the selectivity toward aromatics increase. The dehydrogenation of propane over GeO₂/SiO₂ at 773 K and the n-heptane transformation overH-ZSM5 and Ge/H-ZSM5 at 673 K were performed. Results confirm the dehydrogenation capacity of GeO₂ and show similar activity and selectivity for n-heptane conversion on H-ZSM5 and Ge/H-ZSM5. The acidic properties of the catalysts were determined by TPD/NH₃ and IR/Pyanalyses. Results show that both the total and strong acidity decrease with the addition of germanium. Therefore, it seems that germanium affects the activity of propane conversion due to the dehydrogenation capacity of GeO₂,while the selectivity toward aromatics decreases due to the lower capacity of cyclization, by decreasing the acidity and the number of strong acid sites. In contrast, the Pt-Ge/H-ZSM5 catalyst presents the highest selectivity toward aromatics (53.4%) which is attributed to the decrease in hydrogenolysis capacity of platinum. The TPR results of the Pt-Ge/H-ZSM5 catalyst indicate interaction of Pt-Ge, and from the hydrogen consumption it was seen that Ge⁴⁺ is partially reduced to Ge²⁺, which is attributed to the presence of metallic platinum. This revised version was published online in July 2006 with corrections to the Cover Date.     

Selective conversion of propane to propene by the catalytic oxidative dehydrogenation over cobalt and magnesium molybdates

Catalytic performances of various metal molybdates were tested in the oxidative dehydrogenation of propane to propene with molecular oxygen under an atmospheric pressure. Most of the molybdates tested promoted the selective oxidative conversion of propane to propene and among them cobalt and magnesium molybdates were found highest in the activity and selectivity. It was also found that their catalytic activities were highly sensitive to the catalyst composition, and it turned out that Co_0.95MoO _x and Mg_0.95MoO _x catalysts which have slightly excess molybdenum showed the highest activity in the oxidative dehydrogenation of propane. Under the optimized reaction conditions, higher reaction temperatures and lower partial pressures of oxygen, these catalysts gave 60% selectivity to propene at 20% conversion of propane. Since the molybdates having the surface enriched with molybdenum oxide tended to show high activity for the propane oxidation, surface molybdenum oxide clusters supported on metal molybdate matrix seem to be the active sites for the selective oxidative dehydrogenation of propane.     

Oxidative dehydrogenation of propane over magnesium molybdate catalysts

Catalytic activities of magnesium molybdates were investigated for the oxidative dehydrogenation of propane with and without molecular oxygen under atmospheric pressure. Catalytic properties drastically changed with the catalyst composition, and it turned out that Mg_0.95MoO_x catalysts having slight excess molybdenum showed the highest activity in the oxidative dehydrogenation of propane, which gave 61% selectivity to propene at 22% conversion of propane at 515°C. The catalytic activities strongly depended on the acidic properties of the catalysts. It was also revealed that the lattice oxide ions of the catalysts participated as an active oxygen in the oxidative dehydrogenation of propane.     

Low-Temperature SCR of NO with NH3 over USY-Supported Manganese Oxide-Based Catalysts

A series of catalysts of manganese oxide, manganese–cerium and iron–manganese oxide supported on USY (ultra-stable Y zeolite) were studied for the low-temperature selective catalytic reduction (SCR) of NO with ammonia in the presence of excess oxygen. It was found that MnO_x/USY have high activity and high selectivity to N₂ in the temperature range 80-180 °C. The addition of iron and cerium oxide increased NO conversion significantly although the single-component Fe/USY and Ce/USY catalysts had low activities. Among the catalysts studied in this work, the 14% Ce-6% Mn/USY showed the highest activity. The results showed that this catalyst yielded nearly 100% NO conversion at 180 °C at a space velocity of 30 000 cm³ g^-1 h^-1. The only product is N₂ (with no N₂O) below 150 °C. The effects of the concentration of oxygen, NO and NH₃ were studied and the steady-state kinetics were also investigated. The reaction order is 1 with respect to NO and zero with respect to NH₃ on the 14% Ce-6% Mn/USY catalyst at 150 °C.     

Oxidative dehydrogenation of propane on zeolite catalysts

Oxidative dehydrogenation of propane has been studied on zeolite Na-Y, stabilized zeolite Y (USY) and ZSM-5. The supports with the faujasite structure were modified with boron, gallium and indium oxides and Ca, Mg, Sn, and Sb cations. The samples containing simultaneously In₂O₃ and Ga₂O₃ in the USY support were compared. A detailed analysis of the zeolite catalysts performance in the title reaction has been carried out.     

Structural effects of WO3 incorporation on USY zeolite and application to free fatty acids esterification

Zeolites have occupied a distinguished position due to their unique properties as solid acids and catalytic results achieved in several industrial reactions. This work studied the influence of supported WO₃ on USY zeolite structure, acidity and activity towards an esterification reaction. High dispersion of WO₃ species on USY was achieved, but at higher loading (?11.4%), microcrystalites of WO₃ were detected below the theoretical monolayer coverage (∼32%). Tungsten species were deposited preferentially inside the zeolite structure and interacted with the Brønsted sites of USY as well as on silanol surface groups with the formation of small aggregates. In addition, dealumination took place, especially in the samples with high WO₃ loading. USY had the most and the strongest acidic sites (Brønsted type), but the incorporation of WO₃ decreased the amount and the strength of the new sites. However, all WO₃/USY catalysts were more active than USY in the esterification of oleic acid with ethanol (conversion above 74%, 2 h at 200 °C). The calculation of the TOF for a 1 h reaction demonstrated that 11.4% WO₃/USY was the most active catalyst. Furthermore, it had the lowest rate of deactivation of acid sites after the reaction (∼13% after four cycles). The better performance of the 11.4% WO₃/USY sample was also attributed to a better distribution of strength of the acidic sites and a more hydrophobic character of the synthesized material.     

USY分子筛上苯与多仲丁苯烷基转移反应

在微型固定床反应器上研究USY分子筛对苯与多仲丁苯烷基转移反应的催化性能,考察反应温度、原料配比和空速等工艺条件对反应的影响。采用NH₃-TPD、吡啶IR吸附和N2吸附-脱附等手段对USY分子筛酸性质和孔结构进行表征。结果表明,USY分子筛在烷基转移反应中具有较好的催化性能,二仲丁苯转化率为87.7%,三仲丁苯转化率为19.3%,仲丁苯选择性为91.38%,与USY分子筛的多级孔道和较多B酸位有关。多仲丁苯转化率和仲丁苯选择性随反应温度的提高而增大,原料中苯的增加可提高仲丁苯选择性,空速对二仲丁苯转化率影响较小,但对仲丁苯选择性和三仲丁苯转化率影响显著。USY分子筛上反应较适宜的工艺条件为：反应温度240 ℃,反应压力3 MPa,苯与二仲丁苯物质的量比16,二仲丁苯空速1.4 h^-1。     

Combined reforming of methane over supported Ni catalysts

The hydrogen exchange for propane-d ₈ adsorbed on zeolite Zn/H-MFI has been studied by¹H MAS NMR spectroscopy in situ within the temperature range of 420–490 K. Kinetic measurements of the H/D exchange between the acidic hydroxyl groups of the zeolite and the adsorbed deuterated propane molecules show that only methyl groups of the alkane are involved in the exchange. Two mechanisms are proposed to rationalize the regioselectivity of the exchange: (i) propane dehydrogenation on Zn-sites followed by protonation of propene by acidic OH groups in accordance to the Markovnikov’s rule and abstraction of deuteride ion from another propane molecule; (ii) the reversible heterolytic dissociative adsorption of propane to form Zn-propyl species and acidic OH groups.     

Selective oxidation of ethane and propane over sulfated zirconia‐supported nickel oxide catalysts

The oxidative dehydrogenations of ethane and propane were investigated over a series of zirconia and nickel‐oxide supported on zirconia catalysts. It was found that zirconia, sulfated zirconia as well as NiO‐based zirconia catalysts showed high catalytic activities for oxidative dehydrogenation of ethane and propane. However, conversion and selectivity differed depending on the nature of the catalysts. Zirconia, sulfated zirconia (SZ) and their supported NiO catalysts showed high ethane conversions but lesser selectivities to olefins while NiO/Li₂ZrO₃ exhibited high selectivities to ethylene and propylene. Addition of an LiCl promoter in the NiO/SZ catalyst increased the catalytic activity and olefin selectivity, thus resulting in a higher olefin yield. In the oxidative dehydrogenations of ethane and propane NiO–LiCl/SZ exhibited 79% ethylene selectivity at 93% ethane conversion at 650 °C and 52% selectivity to propylene at 20% propane conversion at 600 °C, respectively. Characterization showed that the physico‐chemical properties of the catalysts determine the catalytic activity and selectivity. © 2001 Society of Chemical Industry     

Effect of temperature on the product selectivity and aromatics distribution in aromatization of propane over H-GaAlMFI zeolite

The influence of temperature on the product selectivity, aromatics distribution, p-X/o-X and p-X/m-X product ratios, aromatization/cracking and aromatization/dehydrogenation ratios have been exhaustively investigated on H-GaAlMFI at different iso-conversions of propane. These studies show a profound influence of temperature on the product selectivity/distribution of the propane aromatization reaction. The aromatization activity of the H-GaAlMFI zeolite decreases at higher temperatures relative to the cracking and dehydrogenation activities. The benzene selectivity increases whereas the toluene and C₈ selectivity decreases with increasing reaction temperature. The product selectivity and the formation of xylene isomers are kinetically controlled.     

Oligomerization of isobutene over aluminum chloride-loaded USY zeolite catalysts

Oligomerization of isobutene has been investigated over AlCl₃-loaded USY zeolite catalysts in order to produce triisobutenes or remove/separate isobutene from C₄ streams. Stable isobutene conversion and high selectivity for trimers and tetramers were attained over the modified zeolite with high ratio of Lewis acid site-to-Brønsted acid site, suggesting that a potential trimerization catalyst can be obtained easily by loading a Lewis acid into an acidic zeolite catalyst. This catalyst can be facially produced by physical mixing and can be easily restored its activity after deactivation by simple calcinations.     

Catalytic oxidation of propane over molybdenum-based mixed oxides

Catalytic oxidation of propane to produce propene was investigated over molybdenum-based mixed oxide catalysts. Cobalt or magnesium oxide combined with molybdenum oxide exhibits the best catalytic performance for the oxidative dehydrogenation of propane. Catalytic activities of both Co-Mo-O and Mg-Mo-O vary drastically on the catalyst composition and Co(Mg)_0.95Mo_1.0O_x having small amounts of free MoO₃ on the Co(Mg)MoO₄ surface shows the highest catalytic activity keeping a considerably high selectivity to propene. The catalytic activity also depends strongly on the acidic properties of catalysts and MoO₃ clusters formed on the surface of Co(Mg)MoO₄ are responsible for the activities for the oxidative dehydrogenation of propane.     

正庚烷在改性USY负载杂多酸催化剂上加氢异构化反应

在微型固定床催化反应器上考察了改性USY沸石负载杂多酸及贵金属Pt的双功能催化剂上正庚烷加氢异构化反应性能。结果表明,负载杂多酸后的催化剂的催化活性明显提高。金属负载质量分数分别为0.4％、0.8％的改性USY沸石负载杂多酸催化剂,其正庚烷稳定转化率分别提高了7.0％和27.9％,达到37.9％和47.2％,且异构化产物选择性仍保持较高水平。     

Gas-phase chlorination of aromatics over FAU- and EMT-type zeolites

Three FAU-structure type zeolites (EMC-1, USY and USY without EFAl) with different Si/Al molar ratio and their pure hexagonal analogue, the EMC-2 zeolite (EMT-structure type) were prepared and thoroughly characterized. Their catalytic properties were examined in the non-conventional gas–solid reaction requiring a strong acidity. A deeper focus was paid to the difference in activity/selectivity of these zeolites toward the continuous chlorination of aromatics (nitrobenzene and toluene) using trichloroisocyanuric acid (TCCA, C₃N₃O₃Cl₃) as chlorination agent.     

Oxidative dehydrogenation of propane over fluorine promoted rare earth-based catalysts

Catalysts based on rare earth complexes such as CeO₂/2CeF₃, Sm₂O₃/4CeF₃, Nd₂O₃/ 4CeF₃ and Y₂O₃/4CeF₃ were prepared. These catalysts were active for the oxidative dehydrogenation of propane with very high selectivity to propene. At 500°C and 6000 h^–1, using CeO₂/2CeF₃ as the catalyst, the conversion of propane was 41.3%, selectivity to propene reached 81.1%, propene yield was 33.5%. XRD results indicated that F^– and O^2– were exchanged in the lattices. Raman spectra showed that the O ₂ ^– might be the active oxygen species in propane oxidative dehydrogenation.     

Sorption of nitrogen,oxygen, and argon in Cd (II) exchanged zeolite X: volumetric equilibrium adsorption and grand canonical Monte Carlo study

The adsorption of nitrogen, oxygen and argon has been studied in cadmium (II) cations exchanged zeolite X at 288.2 and 303.2 K. Experimentally measured adsorption isotherms are compared with theoretically calculated data using grand canonical Monte Carlo (GCMC) simulation. Nitrogen showed higher adsorption capacity and selectivity than oxygen and argon in these zeolite samples. The cadmium exchanged zeolite X was showed that increased adsorption capacity for nitrogen, oxygen, and argon with increase in Cd (II)-exchange levels, indicating as charge density increases adsorption capacity also increase. Isosteric heat of adsorption data showed stronger interactions of nitrogen molecules with cadmium cations in zeolite samples. These observations have been explained in terms of higher electrostatic interaction of nitrogen with extra framework zeolite cations. The selectivity of oxygen over argon is explained in terms of its higher interaction with Cd (II)-exchanged zeolites than argon molecules. The selectivity of N₂/O₂ of cadmium-exchanged zeolite X is better than only sodium containing zeolite-X. Heats of adsorption and adsorption isotherms were also calculated using GCMC simulation algorithm. Simulation studies expectedly show the proximity of nitrogen molecules to the locations of extra framework sodium and cadmium cations.     

Effects of steaming-made changes in physicochemical properties of Y-zeolite on cracking of bulky 1,3,5-triisopropylbenzene and coke formation

The effects of acidic properties and structural changes of Y zeolite, produced by steaming, on the zeolite cracking activity, coking tendency and distribution of various products during catalytic conversion of bulky 1,3,5-triisopropylbenzene (TIPB) are reported. NaY zeolite with framework Si/Al ratio of 2.4 was synthesized by a hydrothermal method and ammonium exchanged. The zeolite was dealuminated by a temperature-programmed steaming to form USY1 and USY2 zeolites with framework Si/Al ratio of 8.1 and 12.3 respectively. The catalysts were characterized by XRD, XRF, SEM, AAS, NH₃–TPD and N₂ adsorption–desorption techniques. The samples were in-situ activated at 748 K and evaluated by TIPB cracking at 623 K. The coke content of the catalyst beds was estimated by TPO using an FT-IR gas cell. The results of activity measurements reveal that the dealuminated zeolites lead to lower cracking activity initially; while, they exhibit higher activity at longer times. In addition, a slight modification of the window diameter of Y zeolite, as revealed by pore size distribution analyses, alters the diffusion limitation of the reactant and products through the pores of the zeolite and significantly affects the adsorbent–adsorbate interactions. TPO experiments show that compared to the precursor zeolite, lower amount of coke is formed on the dealuminated catalysts possessing lower density of acid sites. However, the coke formed on USY samples is heavier than that formed on its precursor Y zeolite. This may be attributed to the larger pores shaped in the dealuminated catalysts which in turn provide suitable places for coke formation and growth.     

Proton‐poor, gallium‐ and indium‐loaded zeolite dehydrogenation catalysts

The catalytic (propane dehydrocyclization) and reduction behaviors of near 1:1 cation (Ga, In)/framework‐Al MFI zeolites were examined under conditions where the materials were initially either in fully protonated or zero−protonated states. Reductions at appropriate temperatures proceeded up to ∼100% exchange of protons for reduced univalent cations. Further aqueous exchange of alkali (K⁺>) or alkaline earth (Ba²⁺) cations increased the selectivity for dehydrogenation reactions at little or no sacrifice in overall activity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Oxidative dehydrogenation of ethane and propane over Mn-based catalysts

The catalytic performances of Mn-based catalysts have been investigated for the oxidative dehydrogenation of both ethane (ODE) and propane (ODP). The results show that a LiCl/MnO_x/PC (Portland cement) catalyst has an excellent catalytic performance for oxidative dehydrogenation of both ethane and propane to ethylene and propylene, more than 60% alkanes conversion and more than 80% olefins selectivity could be achieved at 650°C. In addition, the results indicate that Mn-based catalysts belong to p-type semiconductors, the electrical conductivity of which is the main factor in influencing the olefins selectivity. Lithium, chlorine and PC in the LiCl/MnO_x/PC catalyst are all necessary components to keep the excellent catalytic performance at a low temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

Modulation of ODH Propane Selectivity by Zeolite Support Desilication: Vanadium Species Anchored to Al-Rich Shell as Crucial Active Sites

The commercially available zeolite HY and its desilicated analogue were subjected to a classical wet impregnation procedure with NH₄VO₃ to produce catalysts differentiated in acidic and redox properties. Various spectroscopic techniques (in situ probe molecules adsorption and time-resolved propane transformation FT-IR studies, XAS, ⁵¹V MAS NMR, and 2D COS UV-vis) were employed to study speciation, local coordination, and reducibility of the vanadium species introduced into the hierarchical faujasite zeolite. The acid-based redox properties of V centres were linked to catalytic activity in the oxidative dehydrogenation of propane. The modification of zeolite via caustic treatment is an effective method of adjusting its basicity—a parameter that plays an important role in the ODH process. The developed mesopore surface ensured the attachment of vanadium species to silanol groups and formation of isolated (SiO)₂(HO)V=O and (SiO)₃V=O sites or polymeric, highly dispersed forms located in the zeolite micropores. The higher basicity of HY_deSi, due to the presence of the Al-rich shell, aided the activation of the C−H bond leading to a higher selectivity to propene. Its polymerisation and coke formation were inhibited by the lower acid strength of the protonic sites in desilicated zeolite. The Al-rich shell was also beneficial for anchoring V species and thus their reducibility. The operando UV-vis experiments revealed higher reactivity of the bridging oxygens V-O-V over the oxo-group V=O. The (SiO)₃V=O species were found to be ineffective in propane oxidation when temperature does not exceed 400 °C.