Abstract:
The aim of this work was the development and testing of supported rhodium catalysts for hydrocarbon production by CO hydrogenation. Four different catalysts were prepared by sequential or co-impregnation to incipient wetness of δ-Al2O3 and SiO2 supports, namely 2wt%Rh/δ-Al2O3 and 1.5wt%Rh/SiO2 in addition to La and V promoted catalysts, 1.5wt%Rh-2.6wt%La/SiO2 and 1.5wt%Rh-2.6wt%La/1.5wt%V/SiO2. Experimental plan included a parametric study of reaction temperature and contact time (W/FCO) as well as effects of support material and promoters on CO conversion. The reaction system used in the experiments consisted of mass flow controllers for gases, a down-flow micro-reactor located in a temperature-controlled furnace, traps, heated stainless steel connecting lines and two on-line gas chromatographs for feed and product analysis. Parametric studies were first conducted on 2wt%Rh/δ-Al2O3 and 1.5wt%Rh/SiO2 using a fixed inlet composition of 10 mol% CO, 20 mol% H2 and balance N2 for W/FCO ratios of 0.49-1.30 mg.min.μmol-1 at 270oC and atmospheric pressure. Subsequent experiments were performed at 230-290oC using various W/FCO ratios in the same range over both non-promoted and singly or doubly-promoted Rh/SiO2. Silica-supported catalyst samples were characterized by X-ray diffraction (XRD), surface area (BET) analysis, and environmental scanning electron microscopy (ESEM) with energy dispersive X-ray analysis (EDX) techniques. Increasing contact times, increasing reaction temperatures and addition of La or La-V promoters all improved catalytic activity (CO conversion) significantly. Among the catalyst samples tested for CO hydrogenation, doubly-promoted 1.5wt%Rh-2.6wt%La/1.5wt%V/SiO2 catalyst yielded the highest CO conversion. Since reaction tests were conducted at atmospheric pressure, methane was the major product observed in all cases.
