RESUMO
We investigated the possibility of synthesizing Co nanoparticles in CoZrnH/AlOx(OH)y/Al ceramic-metal catalysts and controlling the catalytic properties of these nanoparticles in syngas conversion by changing the Co/Zr ratio. The CoZr nanocomposites were obtained from metal powders by mechanochemical activation in a high-energy mill under an argon atmosphere, followed by treatment with hydrogen at high pressure and room temperature. Ceramic-metal catalysts were prepared by mixing the corresponding CoZrnH powder nanocomposite (30 wt%) with powdered aluminum (70 wt%), hydrothermal treatment of the mixture and subsequent calcination. The materials were characterized with a set of physicochemical methods: powder X-ray diffraction, scanning electron microscopy, 59Co internal field nuclear magnetic resonance spectroscopy, and temperature programmed reduction. Catalytic studies were performed in a laboratory fixed-bed flow reactor at 2 MPA and 210-270 °C. It is shown that the activity in syngas conversion to C5+ hydrocarbons and selectivity to methane and C2-C4 hydrocarbons depend on the Co/Zr ratio. Thus, with an increase in the zirconium content in the samples, the interaction of metal cobalt with metal zirconium improves in the process of mechanical activation and subsequent treatment with hydrogen. The destruction of the agglomerates of crystallites of metallic cobalt in the form of ß-Co (Cofcc) occurs as well as their transformation to α-Co (Cohcp) particles active in the syngas conversion to C5+ hydrocarbons. This can explain the highest specific yield of C5+ hydrocarbons on a cermet with the lowest Co/Zr ratio.
RESUMO
Highly dispersed LaCo1-x-yCuxTiyO3/KIT-6 perovskites were synthesized by the citrate method with inert mesoporous KIT-6 addition. The KIT-6 matrix was removed by dissolution in 7% NaOH aqueous solution. The dispersity of perovskites probably varies depending on the largest cation and its content at the B position of the perovskite ABO3 structure. The CoS=23+/CoS=03+ ratio increases with the increase in copper content and in the presence of Ti4+. It may be explained by the compensation of the distortion of the perovskite structure. The maximum syngas conversion is achieved at nCo/nCu = 7/3. At a higher copper content, the activity of the samples decreases due to the formation of large copper particles (up to 40 nm) in the course of the reduction. The selectivity for alcohols increases with an increase in the proportion of copper and reaches maximum values at a ratio of nCo/nCu close to 1. The distribution of alcohols is the same for all samples, except for LaCo0.35Cu0.35Ti0.3O3/KIT-6. It can be assumed that the synthesis of alcohols proceeds on bimetallic CoCu particles 3 nm in size and cobalt particles 4-6 nm in size, most likely enriched with copper on the surface.
