Mechanisms of catalytic activity in heavily coated hydrocracking catalysts

Catalyst deactivation by coke deposition has a direct impact on the economic viability of heavy hydrocarbon upgrading processes, such as coal liquefaction and oil residue hydroprocessing. The effect of carbonaceous deposition on the catalytic activity of a chromium pillared montmorillonite was studied. The catalytic activity in hydrocracking a coal extract was evaluated based on the boiling point distributions of feed and products obtained. CM3, a Cr-pillared montmorillonite, exhibited an interesting level of hycrocracking activity, comparable to that of a NiMo/Al₂O₃ commercially used. The pillared clay retained its activity even though it showed high carbon loading, a large drop in surface area and complete apparent pore blockage. Some observations that may contribute to explain the persistent catalytic activity were discussed. Hydrogenation on the active sites would make the deposits more soluble in the liquid clearing a surrounding area from deposits.