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Abstract: A series of vanadia-alumina catalysts with different vanadia contents were prepared by a wet impregnation method. The influence of the local structure of vanadia in these catalysts on the oxidative dehydrogenation of ethylbenzene with nitrous oxide was investigated. The use of N2O as a co-feed remarkably enhanced the styrene yield compared with the use of N2. Characterization of these vanadia catalysts by XRD, FTIR, UV–vis, TPR, XPS, and 51V NMR techniques suggests that the nature of the VO x species depends on the vanadia loading; the predominant species are monomeric vanadia at lower loadings, two-dimensional polyvanadates at intermediate loadings, and bulk-like V2O5 and AlVO4 at higher loadings. The rate of oxidative dehydrogenation (ODH) of ethylbenzene per vanadium atom increases with vanadia loading and reaches a maximum at 10 wt%, the loading at which the surface predominantly contains polyvanadate species. The observed variation in the selectivity of products with vanadium loading indicates that the monomeric V5+ species favors dehydrogenation, whereas bulk-like V2O5 preferentially participates in the dealkylation of ethylbenzene. The vanadium species remains at a higher oxidation state in the presence of N2O, leading to a higher styrene yield, than in a N2 atmosphere. The ODH turnover rates increased with decreasing energy of the absorption edge in the UV–vis spectrum, at low VO x coverages of less than one monolayer on the Al2O3 surface. [Copyright &y& Elsevier]

The protonic forms of zeolite beta (H/β) with different crystallinities were obtained by postsynthesis modification of phases that were obtained by varying crystallization periods during progressive crystallization from a (TEA)2O–Na2O–SiO2–Al2O3–H2O system at 413 K. These catalytic materials were characterized using powder X-ray diffraction, 27Al MAS NMR, nitrogen adsorption, temperature-programmed ammonia desorption (TPAD), sorption of benzene probe molecules, and chemical composition. Evaluation of the catalysts for isopropylation of benzene reaction using isopropanol as alkylating agent was carried out in a continuous, down–flow, fixed-bed reactor at 483 K, liquid hour space velocity (LHSV) of 2.5 h-1, and feed (isopropanol: benzene) molar ratios ranging from 1:6.5 to 4:6.5. The effect of time on stream on the benzene conversion and cumene selectivity was also studied. The pore volume accessible to benzene in catalyst was found to provide a more realistic measure for screening the catalyst as compared to percentage XRD crystallinity. A catalyst, which is XRD amorphous in nature, has exhibited nearly 27% benzene conversion and 48% cumene selectivity when compared with fully crystalline catalyst. Cumene selectivity was found to increase with increase in time on stream when the feed used contained a IPA/benzene molar ratio below 0.31. The number of strong Brönsted acid sites was found to increase with the increase in the crystallinity up to 85% XRD crystallinity. Above 85% XRD crystallinity, no considerable improvement was observed in catalyst activity as far as benzene conversion and cumene selectivity are concerned. [Copyright &y& Elsevier]