Synthesis of tetrahedrally coordinated CoO for higher alcohol synthesis directly from syngas

Abstract

Higher alcohol synthesis directly from syngas is highly desirable as one of the efficient non-petroleum energy conversion routes. Co⁰–CoO catalysts showed great potential for this reaction, but the alcohol selectivity still needs to be improved and the crystal structure effect of CoO on catalytic behaviors lacks investigation. Here, a series of tetrahedrally coordinated CoO polymorphs were prepared by a thermal decomposition method, which consisted of wurtzite CoO and zinc blende CoO with varied contents. After diluting with SiO₂, the catalyst showed excellent performance for higher alcohol synthesis with ROH selectivity of 45.8% and higher alcohol distribution of 84.1 wt % under the CO conversion of 38.0%. With increasing the content of wurtzite CoO, the Co⁰/Co²⁺ ratio gradually increased in the spent catalysts, while the proportion of highly active hexagonal close packed cobalt in Co⁰ decreased, leading to first decreased then increased CO conversion. Moreover, the higher content of zinc blende CoO in fresh catalyst facilitated the retention of more Co²⁺ sites in spent catalysts, promoting the ROH selectivity but slightly decreasing the distribution of higher alcohols. The catalyst with 40% wurtzite CoO obtained the optimal performance with a space time yield toward higher alcohols of 7.9 mmol·g_cat⁻¹·h⁻¹.