Isopropylation of benzene catalyzed by H/β zeolite catalysts with different crystallinities

The protonic forms of zeolite beta (H/beta) with different crystallinities were obtained by postsynthesis modification of phases that were obtained by varying crystallization periods during progressive crystallization from a (TEA)(2)O-Na2O-SiO2-Al2O3-H2O system at 413 K. These catalytic materials were characterized using powder X-ray diffraction, Al-27 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 Bronsted 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. (C) 2004 Elsevier Inc. All rights reserved.