Influence of the Preparation Procedure on the State of Platinum and on the Isomerizing Ability of Catalysts for Isodewaxing of High-Molecular-Mass Hydrocarbon Feedstock

Abstract

Granulated catalytic materials based on Al₂O₃ + SAPO-11 with Pt deposited either onto Al₂O₃ with the subsequent mixing with SAPO-11 or onto granulated composite support Al₂O₃ + SAPO-11 were prepared. The catalyst supports were prepared with the addition of polystyrene template to the mixture of support precursors or without template. The materials were characterized by Fourier IR spectroscopy of adsorbed pyridine, mercury and nitrogen porosimetry, X-ray diffraction analysis, inductively coupled plasma atomic emission spectroscopy, electron microscopy, and CO chemisorption. In all the samples, platinum was uniformly distributed over the granule cross section. The most pronounced platinum aggregation was observed in supports prepared without template and in those prepared by admixing SAPO-11 to Pt/Al₂O₃ (compared to the deposition onto the composite support). The template catalysts are characterized by increased CO/Pt stoichiometry (according to the СО chemisorption data) and larger particle size (according to electron microscopy data), which is due to high surface defectiveness and formation of Pt particles of unusual flat morphology. Strong metal–support interaction in these samples was confirmed by the presence of high-temperature H₂ uptake peaks (above 750°С) in the temperature-programmed reduction (TPR) experiments; such peaks were absent in the TPR spectra of the analogs prepared without template. The template samples have also high total specific pore volume (0.6–0.8 cm³/g). Catalytic trials have shown that, under the conditions of the С₁₈₊ feed dewaxing, the target liquid product is formed exclusively in the presence of catalysts prepared by the template procedure, which demonstrates essential advantage of this approach and apparent shift of the process toward isomerization.