CoCu/SiO2 catalysts via galvanic replacement for CO hydrogenation to higher alcohols
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Higher alcohols can be synthesized from syngas (CO/H2) with a CuCo catalyst, however no catalyst was sufficient in performance and reproducibility to reach past the pilot plant stage. A criterion for improving the selectivity towards higher alcohols is the intimacy between both metals, which can be attained with galvanic replacement. In this work, the synthesis of CuCo catalysts via galvanic replacement of pre-deposited Co nanoparticles on SiO2 by Cu ions is investigated to gain better understanding and control over the Cu deposition. Various Cu precursors and solvents were used to determine their effects on the galvanic replacement reaction. Use of organic solvents for galvanic replacement yielded low Cu deposition and leaching of Co as determined by ICP. Galvanic replacement with aqueous Cu2+ solutions yielded excellent Cu deposition and is the most promising for catalyst synthesis, however irreducible Co silicates were formed rendering this catalyst inactive. The intimacy between Cu and Co was determined with (S)TEM-EDX and XRD. The catalytic performance and stability of each catalyst was evaluated in the CO hydrogenation reaction. The higher alcohol selectivity of the active catalysts was up to 6%, however primarily hydrocarbons were formed (around 90%). The catalysts synthesized via galvanic replacement showed a notably lower selectivity towards methanol compared to a catalyst prepared via conventional co-impregnation, suggesting a better metal intimacy. This work presents a step forward towards a better higher alcohol synthesis catalyst, however the next challenge that needs to be addressed is the formation of Co silicates when aqueous solutions are used.