A novel family of solid acid catalysts: substantially amorphous or partially crystalline zeolitic materials

Hydrogels, typically used for the synthesis of highly crystalline ZSM-5 sam ples at 150 degrees C and under autogenous pressure, were subjected to lowe r hydrothermal synthesis temperatures, i.e., from 25 degrees C to 130 degre es C. XRD analysis of the samples obtained at the various temperatures show ed that for synthesis temperatures of up to 70 degrees C, X-ray amorphous a luminosilicates were obtained, whereas treatment at 90 degrees C produced a material exhibiting a 2% XRD crystallinity. Higher synthesis temperatures resulted in higher levels of % crystallinity. Evaluation of the samples as catalysts for the skeletal isomerization of linear butenes was carried out in a flow reactor at 500 degrees C, MHSV=3 and a butene:nitrogen dilution o f 1:10. The results showed that the % conversion of the linear butenes incr eases and the % selectivity to isobutene decreases with increasing autoclav e synthesis temperature, with the highest yield of isobutene (23.4%) being achieved with the 2% XRD crystallinity sample. Higher crystallinities produ ced considerably lower yields of the branched alkene. The catalytic propert ies of the 2% XRD crystallinity sample were further evaluated as a function of reaction temperature, 350-500 degrees C, at MHSV=1 and a dilution of 1: 10. Highest yield of isobutene was obtained at 500 degrees C and under thes e reaction conditions, the sample exhibited stable catalytic performance (3 1% yield) for up to 40 h on-stream. In contrast, under the same reaction co nditions, an 86% crystalline ZSM-5 sample gave a 4.9% yield of isobutene. W ork on partially crystalline ferrierite-based materials as catalysts for th e same reaction was also carried out. (C) 1999 Elsevier Science B.V. All ri ghts reserved.