Mechanochemical approach for the preparation of technical catalysts

Abstract

Technical catalysts are shaped as pellets, extrudates, beads, and monoliths. Most often, they are composed of a mixture of oxides used as carriers for metallic phases. The latter are usually incorporated by wet impregnation; a method with a strong environmental impact due to the production of liquid wastes and toxic gases. Owing to such issues, this work presents alternatives for preparing technical catalysts using reactive grinding to mix its components. Particularly, we prepared a series of catalytic extrudates used in the hydrocracking of tetralin. These extrudates were composed of a bimetallic NiMo active phase, an acidic HY zeolite, and boehmite as a binding agent. A 25 wt% combination of HY zeolite with boehmite was used as the carrier for the NiMo active phase. The need for the inclusion of a calcination step for the preparation of the carrier was examined as well as the need for the use of a simultaneous or sequential impregnation process for incorporating the metallic NiMo phase into the carrier. In general, we demonstrate that there is no need for calcining the carrier. Indeed, non-calcined carriers produced catalysts with higher mechanical resistance than the catalysts whose carrier was calcined. In addition, we found that the simultaneous impregnation of NiMo yields materials with better catalytic properties than both their sequentially impregnated and wet-impregnated counterparts. This tendency was ascribed to the preservation of the crystallinity of the zeolite; a better dispersion and exposure of the HY zeolite within the matrix of the carriers which preserve its acidity when the NiMo phase is present. Overall, we also demonstrated that an adequate fluency of the extrusion pastes can be achieved using only water as lubricant. These findings are of course a step forward in the search for less environmentally harmful processes for catalysts manufacturing.