Synthesis of highly-uniform titania overcoats on a mesoporous alumina catalyst support by atomic layer deposition and their application in hydroprocessing

Abstract

The feasibility of gas phase deposition using a Ti alkoxide precursor for precise surface modification of catalysts was demonstrated by modifying a mesoporous alumina support with a Ti oxide overcoat. Titanium tetra-isopropoxide yields a Ti oxide layer that covers homogeneously the alumina surface. Uniformity of the deposited TiO₂ was verified by SEM-EDX, on both intra-particle and inter-particle levels. Only a few atomic layer deposition (ALD) cycles were required in order to obtain Ti contents with a relevance for industrial application. The pore size distribution of the overcoated catalyst support was barely affected by the coating process. Synthesized CoMo catalysts based on the Ti-alumina carrier showed up to 40% higher activity compared to a catalyst supported on pristine alumina, in hydroprocessing under industrial testing conditions. The TiO₂ coating appeared to be stable, showing no agglomeration characteristics after reaction as corroborated by TEM-EDX. ALD provides a scalable route with low waste generation for the production of precisely structured TiO₂–Al₂O₃ hydroprocessing catalyst supports.