Ni/hydrotalcite catalysts are synthesized by the coprecipitation method. Synthesis times are decreased and activation is performed with just a reductive calcination under mild conditions without the usual air‐calcination step. Compared with the other reported catalysts made of Ni/hydrotalcite, in terms of space–time yield (STY), the best synthesized catalyst is the most efficient one (STY = 137.19 mol CH4 h−1 L−1 at 300 °C) and this high efficiency is kept at low temperature (STY = 132.67 mol CH4 h−1 L−1 at 250 °C). Results show that the amount of reduced Ni, created upon the mild reduction, increases with the Ni loading and the Ni0 amount correlates with the catalytic activity. CO2 adsorption capacity remarkably increases with the Ni content but this trend does not correlate with the conversion. Surface areas, neither pore sizes, do not show a correlation with catalytic results. The most important result is the very high activity observed at temperatures below 300 °C. Characterization results indicate that the outstanding low‐temperature performance must be due to the presence of high amounts of small and reduced Ni crystallites with low interaction with the support. Developed catalysts are stable for 28 h at 300 °C.
Cyclohexanol and 1-methyl-1,2-cyclohexanediol were produced via the hydrotreating of guaiacol, using new hydrotalcite-based nickel (HT-Ni-R) and cobalt (HT-Co-R) catalysts.. Guaiacol is the most representative model compound for lignin-derived bio-oils. Catalysts were prepared by co-precipitation of the metals (Mg-Al, Ni or Co) followed by direct reduction with H2 at high temperature (550°C). Active species are highly dispersed Ni0 and Co0 particles formed upon reduction of part of the Ni2+ and Co2+. The main effect of the new synthesis procedure is to remarkably increase the dispersion of these metal particles, compared to those on the supported catalysts. Cobalt catalyst is more efficient for oxygen removal than the nickel catalyst, but this latter is more efficient for aromatic´s hydrogenation. HT-Ni-R produced 1-methyl-1,2-cyclohexanediol as the main product (70%). The main reaction pathway with HT-Co-R was the formation of cyclohexanol (41%). The high metal dispersion induced by the proposed synthesis procedure is the most important advantage of the new catalysts allowing the obtention of products with added value from potential renewable resources as lignin.
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