Hydrocarbon conversion catalysts

In this study we have shown that the catalytic method—carbon deposition during hydrocarbons conversion—can be widely used for nanotubule production methods. By variation of the catalysts and reaction conditions it is possible to optimize the process towards the preferred formation of hollow... 

Hydrocarbon conversion with acidic multimetallic catalytic composite Production of catalysts 87... 

Hunger, M. and Horvath, T.J. (1995) A new mas NMR probe for in-situ investigations of hydrocarbon conversion on solid catalysts under continuous-flow conditions, Chem. Soc. Client. Comm., 14, 1423. 

Robson, A. Synthetic Halloysite as Hydrocarbon Conversion Catalysts, US Patent 4,098,676. 

The higher the fuel temperature is, the higher the parent hydrocarbon conversion is (Table 1). For example, without catalyst and at 375 °C, the n-dodecane conversion is 2%, but at 425 °C it raises to 33%. 

Catalytic upgrading of the hydrogen-rich syngas (tar and hydrocarbon conversion, possibly in combination with filtration, also water gas shift catalyst use and... 

A variety of solid acids besides zeolites have been tested as alkylation catalysts. Sulfated zirconia and related materials have drawn considerable attention because of what was initially thought to be their superacidic nature and their well-demonstrated ability to isomerize short linear alkanes at temperatures below 423 K. Corma et al. (188) compared sulfated zirconia and zeolite BEA at reaction temperatures of 273 and 323 K in isobutane/2-butene alkylation. While BEA catalyzed mainly dimerization at 273 K, the sulfated zirconia exhibited a high selectivity to TMPs. At 323 K, on the other hand, zeolite BEA produced more TMPs than sulfated zirconia, which under these conditions produced mainly cracked products with 65 wt% selectivity. The TMP/DMH ratio was always higher for the sulfated zirconia sample. These distinctive differences in the product distribution were attributed to the much stronger acid sites in sulfated zirconia than in zeolite BEA, but today one would question this suggestion because of evidence that the sulfated zirconia catalyst is not strongly acidic, being active for alkane isomerization because of a combination of acidic character and redox properties that help initiate hydrocarbon conversions (189). The time-on-stream behavior was more favorable for BEA, which deactivated at a lower rate than sulfated zirconia. Whether differences in the adsorption of the feed and product molecules influenced the performance was not discussed. 

TBA and isobutene have been compared as the etherifying agent at 60 °C. The initial molar ratio of isobutene to glycerol was 4.0 with Amberlyst A35 as the catalyst. The conversion of glycerol is lower when etherified with TBA than when etherified with isobutene. More hydrocarbons are formed with isobutene than with TBA. But, with TBA, mainly monoethers are formed and valuable triethers are formed only in small amounts. In addition, TBA dehydrates to water, which has an inhibition effect on ion-exchange resin catalysts [23],... 

Attempts to make enzyme-like catalysts, synzymes, from nonbiological systems is described by G. P. Royer. The final two chapters by Y. Yamazaki and T. Kawai, and Z. Paal deal with catalytic hydrocarbon conversions using acids and metals, respectively, as catalysts. 

Control of the multitude of pathways which feed molecules can take is the primary objective of aU catalyst and process developments. The work covered in this chapter focuses primarily on describing the approaches in material and catalysis development which have led to major advances in zeolite application in hydrocarbon conversion. The breaking and formation of carbon-carbon and carbon-hydrogen bonds constitute the majority of the chemical transformations involved here with the less prevalent, but very important, breaking of carbon bonds with sulfur, nitrogen and oxygen taking place in parallel. 

Ceria, particularly when doped with Gd203 or SmzOs," has received some attention for direct hydrocarbon conversion in SOFC. Dating back to Steele and co-workers,interesting properties have been demonstrated for ceria-based anodes in direct utilization of methane. Later work suggested that the performance of ceria-based anodes in hydrocarbons could be improved by the addition of precious-metal catalysts, at dopant levels,but the performance of these cells was still too low for practical considerations. The problem with doped ceria is likely that its electronic conductivity is not sufficient. In general, the electrode material should have a conductivity greater than 1 S/cm in order to be practical since a conductivity of 1 S/cm would lead to a cell resistance of 0.1 Q cm for an electrode thickness of 1 mm, even... 

In an automobile s catalytic converter, CO and hydrocarbons present in the exhaust gases are oxidized. Unfortunately the effectiveness of these units decreases with use. The phenomenon was studied by Summers and Hegedus in /. Catalysis, 51, 185 (1978) by means of an accelerated aging test on a palladium impregnated porous pellet packed bed converter. From the reported data on hydrocarbon conversion shown below, develop an expression to represent the deactivation rate of this catalyst. 

In 1948 Maxted and Walker studied the detoxification of catalyst poisons in the hydrogenation of aromatic hydrocarbons and found that the isomeric thienothiophenes 1 and 2 could be converted into the sul-fones of fully hydrogenated thienothiophenes 1 and 2, which do not poison the catalysts. This conversion is performed by brief preliminary hydrogenation and subsequent oxidation by hydrogen peroxide or per-molybdic acid. However, no data on the isolation or foe properties of these disulfones are available. It has been reported that direct oxidation of thienothiophenes 1 and 2 does not produce sulfones. 

Pfefferle carried out prereforming of JP-4 fuel, feeding a mixture of fuel, H2, and steam with Pt and Rh supported on alumina containing 6% silica at a temperature below 700°C. The presence of H2 in the feed allows prereforming to occur at low temperatures and, subsequently, a S/C ratio as low as 1 can be used without substantial catalyst deactivation. More than 90% hydrocarbon conversion to methane, H2, CO, and CO2 was observed in prereformer without any catalyst deactivation. 

The model includes fundamental hydrocarbon conversion kinetics developed on fresh catalysts (referred to as start-of-cycle kinetics) and also the fundamental relationships that modify the fresh-catalyst kinetics to account for the complex effects of catalyst aging (deactivation kinetics). The successful development of this model was accomplished by reducing the problem complexity. The key was to properly define lumped chemical species and a minimum number of chemical reaction pathways between these lumps. A thorough understanding of the chemistry, thermodynamics, and catalyst... 

Although the reaction classes discussed earlier are sufficient to describe the hydrocarbon conversion kinetics, an understanding of the elementary reaction sequence is needed to describe catalyst deactivation. Several of the overall reactions require formation of olefinic intermediates in their elementary reaction sequence. Ultimately, these olefinic intermediates lead to coke formation and subsequent catalyst deactivation. For example, the ring closure reaction... 

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