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The mechanism of hydrogen transfers from naphthenes (methylcyclohexane, cyclohexane) or their deuterated derivatives to 1-hexene was specified over model acid zeolite catalysts (HREY or HZSM5). The composition of products is determined by two reactions-cracking and intermolecular hydrogen transfer. The monomolecular cracking reaction proceeds mostly on HZSM-5 zeolite, whereas the bimolecular hydrogen transfer reactions are catalyzed by the wide-pore HREY zeolite. It was found that during the hydrogen transfer from the naphthene molecule (hydrogen donor) to the olefin molecule (hydrogen acceptor) only one hydrogen atom is transferred, whereas the second hydrogen atom comes from the Brønsted acid site of the catalyst. [ABSTRACT FROM AUTHOR]

We performed n -heptane cracking over Cu-ZSM-5, Ag-ZSM-5, and P/H-ZSM-5 before and after steaming under various conditions. The reduced Cu-ZSM-5 and Ag-ZSM-5 exhibited similar n -heptane cracking activities to H-ZSM-5 due to generation of Brønsted acid sites by reduction of metal cations. The order of steaming stabilities in the presence of O 2 was Cu-ZSM-5 > Ag-ZSM-5 ≫ P/H-ZSM-5, which was the reverse order of cumene cracking activities in the presence of O 2 . Cumene cracking activity is a function of Brønsted acidity. Therefore, these findings indicate that the steaming stability of a catalyst is strongly related to its Brønsted acidity. Cu 2+ and Cu + cations in the 194%Cu-ZSM-5 were not reduced to Cu 0 at a high temperature of 1023 K in the presence of O 2 and, therefore, 194%Cu-ZSM-5 exhibited an ultra-high steaming stability in the presence of O 2 . The Brønsted acidity of 95%Ag-ZSM-5 was extremely low, almost equal to 194%Cu-ZSM-5. However, the thermal reduction of Ag + took place during steaming even in the presence of O 2 at a high temperature of 1023 K and, therefore, the steaming stability of 95%Ag-ZSM-5 in the presence of O 2 was much lower than that of 194%Cu-ZSM-5. [ABSTRACT FROM AUTHOR]

Abstract: In situ growth of ZSM-5 crystals on the surface of Ni-based alloy supports by hydrothermal synthesis and their mechanical, structural stability were investigated. ZSM-5 crystals grown on the wall of a long (750mm) tubular reactor with a small inner diameter (1mm) was evaluated as a structured catalyst for cracking of n-heptane as a model endothermic fuel. The results have shown that the adhesion strength between ZSM-5 crystals and the support was strong enough to resist a heating/fast-cooling cycle (the sample was immersed into water immediately after being heated to be 750°C). The crystalline structure of ZSM-5 crystals was also stable against the heating/fast-cooling cycle. The structured catalyst was shown to be catalytically active for cracking of n-heptane (LHSV=200h−1) at 700°C. The formation rates of gaseous cracking products were 9.8mlmin−1 and 29.3mlmin−1 for the bare tubular reactor and the tubular reactor with ZSM-5 crystals grown on the wall, respectively. These structured catalysts show high promise for cracking of endothermic fuels at high temperatures. [Copyright &y& Elsevier]

Abstract: The effect and localization of thiophene-like poisons were studied on fluid catalytic cracking (FCC) catalyst at the individual particle level. The thiophene-like poisons interact on the Brønsted acid sites of the catalytic materials, forming oligomeric carbocations and coke species, which absorb and emit light in the visible region. The matrix components are not active in the formation of those light absorbing species. In contrast, zeolite Y and ZSM-5 were very active in inducing oligomer formation and the product distribution was different depending on the zeolite pore structure. Comparison of thiophene results with alkane and alkene catalytic cracking studies reveal that FCC particles have more affinity to react with thiophene molecules compared to n-hexane, but 1-hexene may compete with thiophene in the formation of carbocationic species on Brønsted acid sites. Moreover, a different reactivity was observed in thiophenes with distinct electron withdrawing/releasing substituents and molecular sizes. Our results demonstrate that the carbocations are coke intermediates, and the FCC particles containing zeolite Y promote to a higher extent coke formation: the large supercages allow the accommodation of more bulky coke species. On the other hand, FCC particles containing ZSM-5 stabilize the carbocations within the narrower cylindrical pores, diminishing coke formation. Confocal fluorescence microscopy can resolve the location of sulfur components at the single particle level with submicron resolution. Fluorescence microscopy images reveal heterogeneous domains with highly bright fluorescence across the FCC particles, which are attributed to the selective formation of oligomeric carbocations and coke species on the zeolitic material. The presence of thiophenes with different substituents and sizes was also studied by this approach. This demonstrates the potential of confocal fluorescence microscopy to identify reactivity differences of thiophene-like molecules on FCC catalyst particles in a spatially-resolved manner. [Copyright &y& Elsevier]

Abstract: Effects of Ce0.68Zr0.32O2 physically mixed with or impregnated on amorphous silica–alumina (SA) on enhanced combustion of coke and oxidation of CO formed in the regeneration of the catalysts coked during catalytic cracking of 1,3,5-triisopropylbenzene (TiPB) were studied. SA with about 535m2/g BET surface area was synthesized using a co-precipitation method and ammonium exchanged. 6.0wt% Ce0.68Zr0.32O2 on the silica–alumina was prepared by impregnation of the sample with an aqueous solution of cerium and zirconium nitrates and designated as Ce0.68Zr0.32O2/SA. Nanoparticles of Ce0.68Zr0.32O2, with around 12nm crystallite size, were also prepared by a microwave induced combustion synthesis method and physically mixed with SA as another catalyst sample, i.e. Ce0.68Zr0.32O2·SA. The catalysts were characterized by SEM, EDS, XRD, BET, AAS, H2-TPR and ammonia TPD techniques. After in situ calcination at 475°C for 3h, the samples were coked by exposure to a gaseous stream of 5.0vol% TiPB in Ar at 350°C for 40min. Temperature-programmed oxidation (TPO) method was employed to study the onset temperature of the coke combustion and CO oxidation during the regeneration of the coked catalyst in 2.0vol% O2/N2 feed. At 3min of cracking, TiPB cracking activities of both Ce0.68Zr0.32O2/SA and Ce0.68Zr0.32O2·SA samples are about the same and 5% lower than that of SA. The selectivity of cumene, as a deep cracking product, decreases in the order of SA>Ce0.68Zr0.32O2·SA>Ce0.68Zr0.32O2/SA concomitant with the density of acid sites of the catalysts. As compared to the SA, a decline of about 15.2% in coke formation is observed for the Ce0.68Zr0.32O2/SA sample. In addition, the Ce0.68Zr0.32O2 promotion of SA by physical mixing and impregnation lowers the CO evolution in the catalysts regeneration by about 51 and 61%, respectively. The highly active Ce0.68Zr0.32O2 oxygen is responsible for the higher conversion of CO to CO2 on the catalysts containing the promoter. Furthermore, the Ce0.68Zr0.32O2/SA sample, impregnated with Ce0.68Zr0.32O2 promoter, lowers the onset temperature of coke combustion by about 130°C. This may be attributed to tight contact of the coke with active surface oxygen of the promoter. [Copyright &y& Elsevier]

Abstract: The application of various transient techniques in heterogeneous catalysis (TAP, step-response experiments, SSITKA, TEOM), with the aim to determine reaction kinetics for design purposes, is presented for several cases. These cases, comprising catalytic cracking, diffusion in zeolites, simultaneous NO x and SO x removal, syngas production from methane by chemical looping and selective catalytic reduction of NO x , show that transient techniques can be well used for the purpose of rapid determination of the reaction kinetics without the laborious classical approach of steady-state kinetic measurements and without the need of high levels of sophistication to interpret and process the experimental data. In this respect transient kinetics deserve, next to fundamental catalysis studies, more frequent application in design studies for industrially relevant reaction systems. Topics and challenges for further developments in transient studies are indicated. [Copyright &y& Elsevier]

Abstract: The effect of the introduction of phosphorus on H-MFI zeolite before and after hydrothermal treatment was studied. The samples were characterized by XRF, nitrogen adsorption, 27Al and 31P MAS NMR, n-propylamine temperature-programmed decomposition, n-hexane cracking and vacuum gasoil cracking. Results showed that P stabilizes the MFI zeolite structure by preventing the segregation of the framework Al atoms during the steaming treatment. Although there is an optimum phosphorus content, its effect on the selectivity towards light olefins will depend on the severity of the steaming treatment, i.e., with more severe treatment the stabilization is more evident. NMR results evidenced the presence of several types of aluminium and phosphorus species. Besides the classical framework tetracoordinated Al, which is the main responsible for the acidity of the samples, another tetrahedral aluminium probably in a distorted environment also seems to be active in n-hexane cracking, besides favouring the light olefins production during gasoil cracking. [Copyright &y& Elsevier]

Abstract: Two sets of pillared clays (PILCs), chromia and tin-oxide-pillared montmorillonites and laponites, were successfully prepared at Aston University using both conventional and microwave-assisted methods and characterised by X-ray diffraction and thermogravimetric analysis. Microwave irradiation enabled the preparation of the PILCs in a fraction of time of the conventional methods. X-ray powder diffraction was not a suitable method for characterizing laponite or pillared laponites due to the lack of first order reflections attributed to the small size of individual particles and the random rather than uniform face-to-face orientation of the clay platelets. Laponite appeared to be more thermally stable than montmorillonite. For pillared montmorillonites, dehydroxylation shifted to a lower temperature compared to the starting materials, whereas for tin-oxide-pillared laponites such a shift did not occur. On the other hand for chromia laponite dehydroxylation took place over a much wider temperature range compared to all other materials. The prepared PILCs were employed as catalysts in the hydrocracking of coal-derived liquids in a conventional microbomb reactor at Imperial College exhibiting high-quality performance and remaining active after 4h utilization regardless of high coke deposition. They actually showed an increase in the total conversion when reused. [Copyright &y& Elsevier]

Hydrocracking of petroleum asphaltene with Fe and Ni catalysts loaded on SBA-15 supports has been carried out with a stainless autoclave at 573 K in pressurized H2. Asphaltene conversion with 10 wt.% Fe catalysts with average pore diameters of 4.5–15 nm increases with increasing pore diameter up to 12 nm and reaches about 70%, but levels off beyond this value. Maltene yield shows the same dependency on the diameter and the highest value of 40% at 12–15 nm. When metal loading in the Fe catalyst with the pore diameter of 12 nm is varied between 4 and 30 wt.%, asphaltene conversion and maltene yield are the largest at 4 and 10% Fe, respectively, indicating the presence of the optimum Fe loading for maltene formation. The use of the 10% Ni catalyst in place of the 10% Fe catalyst lowers the conversion slightly but improves selectivity to maltene greatly. This means that the Ni is suitable for selective conversion of asphaltene to maltene, probably because of higher hydrogenation ability. The X-ray diffraction (XRD) measurements of toluene-insoluble (TI) fractions recovered after hydrocracking and the analyses of SO2 evolved during the temperature-programmed oxidation (TPO) reveal the formation of Fe–S and Ni–S phases as surface species. The catalysis of asphaltene conversion by the sulfided forms is discussed. [Copyright &y& Elsevier]

The influence that both the type of matrix and the interaction between zeolite and matrix have on the selectivity of FCC catalysts was studied by means of the conversion of cyclohexene at 300 °C on a large number of samples in which the matrix was changed. Silica/alumina matrices had 0, 12 and 25% of alumina, and catalysts were subjected to steaming of varying severity followed by acid extraction in some samples to remove extraframework aluminum species (EFAl). Resulting catalysts were characterized by various techniques. It was confirmed that hydrogen transfer does not depend directly on the type of coordination of the aluminum atoms in the sample, but rather on the density of paired sites in the zeolite component. It was possible to define the selectivity of reaction pathways (SRP) as an index to describe the relative importance of the processes of desorption via hydride transfer to yield cyclohexane against retention of the cation cyclohexil via isomerization and further reaction. A high value of SRP would mean that a given catalyst has a lower ability to retain adsorbed species that can be subjected to additional reactions like, in this particular reaction, isomerization and further proton transfer to the catalyst surface, or cracking. The index was shown to increase whereas the relative amount of octahedral aluminum atoms decreased, a fact that can be associated to the formation of a new silica/alumina phase. Such phase would be formed by means of the reaction of aluminum extracted from the zeolite upon steaming and silica present in the matrix. [Copyright &y& Elsevier]

In this study, the conversion of HDPE in VGO to fuels was carried out in absence and presence of catalyst. The blend containing 20% HDPE was co-processed in presence of hydrogen at the temperatures of 435 and 450 °C. Five kinds of metal supported on active carbon catalysts (M-Ac) and acidic catalysts (HZSM-5 and DHC-8) were tested. The product distribution and the quality of liquid product changed depending upon the temperature and the type of catalyst. Among the metal supported active carbon catalyst, Co-Ac showed the highest cracking activity where as Mo-Ac showed the highest hydrodesulfurization activity. Co-Ac had better cracking activity than commercial hydrocracking catalyst (DHC-8). Although HZSM-5 had the best cracking effect in the hydrocracking of HDPE/VGO blend, the liquid product from HZSM-5 contained the highest sulphur. The use of carbon-supported metal catalysts in the co-processing of HDPE with VGO looks promising solution from an environmental viewpoint. [Copyright &y& Elsevier]

The significance of hydrogen transport by spillover during diphenylmethane (DPM) hydrocracking in a ceramic membrane reactor has been investigated. In the first part of the study, hydrogen spillover across Al2O3 particles of a ceramic membrane was confirmed by the temperature-programmed hydrogenation (TPH) of coke deposited on SiO2–Al2O3, and placed at the bottom of a layered bed of Co-SiO2 catalyst and Al2O3 membrane particles. CH4 production in the temperature range 430–450 °C was shown to be due to hydrogen activation on the catalyst, spillover across the Al2O3 membrane particles and subsequent reaction with the coked SiO2–Al2O3.The second part of the study focused on the hydrocracking of DPM in a membrane reactor configured so that the catalyst and DPM were separated by a ceramic membrane. Conversion of DPM at temperatures <430 °C was indicative of the reaction between DPM and hydrogen, the latter activated on the catalyst and transferred across the membrane to react with the DPM. Experiments showed that despite the separation of reactant and catalyst, the presence of catalyst enhanced the yield of benzene and toluene compared to thermal cracking at the same reaction conditions. Although contact between liquid and catalyst could not be completely eliminated by the porous ceramic membrane, the yield of benzene and toluene could only be accounted for by the spillover of hydrogen from the catalyst to the membrane, followed by reaction with DPM on the shell-side of the reactor. [Copyright &y& Elsevier]

A vacuum gas oil has been co-fed with nitrogen at different partial pressures in a microacitivity (MAT) unit. The cracking rate versus hydrocarbon partial pressure can be fitted to a first-order kinetic rate equation. On the other hand, hydrogen transfer reactions, which follow second-order kinetics, are more affected than conversion by the decrease in hydrocarbon partial pressure, resulting in an increase in the yield of propylene and in general of LPG olefins. The decrease in conversion, due to the lowering of hydrocarbon partial pressure, could be compensated by a mechanical mixing effect introduced by the dilution gas that improves feed vaporization and mixing.It will be shown that a MAT unit can be used to show both effects separately, i.e. feed dilution and feed dispersion. [Copyright &y& Elsevier]

Hydroisomerization and hydrocracking of n-heptane on Pt-containing HMCM-22, HBeta and on composites with MCM-41 and SiO2 were investigated at 20 bar pressure in the temperature range from 493 to 593 K. The composites showed higher activity and selectivity in isomerization compared to the simple Pt-containing zeolites. The improvement in the catalytic properties was much higher with MCM-22, which has a smaller pore system than with Beta. The higher activity and especially the higher selectivity were explained by the faster adsorption and desorption in the composites. It seems that the transport properties are the most important parameter controlling the final catalyst selectivity. [Copyright &y& Elsevier]