Higher alcohols (HA) have attracted considerable interest owing to their applications as clean gasoline additives, liquid fuels, etc. Nowadays, directly using syngas to produce HA has become a promising technology to develop alternative energy resources. Cu-Co catalyst is regarded as one of the most promising candidates for HA synthesis. It has been reported that Co serve as the main active sites of CO dissociation, while Cu is responsible for CO molecularly adsorption. Thus, the intimate contact between Co and Cu components becomes a key issue in the design and fabrication of HAS catalysts. Here, we proposed a method for constructing highly dispersed Co-Cu bimetallic phases encapsulated in KIT-6 by using ethylene glycol (EG)-assisted impregnation combined with stepwise pyrolysis. On one hand, the EG functions as a "double-bridge" ligand for Cu and Co ions to form Cu-Co-glyoxylate complexes, in which the close contact of Cu and Co active sites could be ensured. On the other hand, EG turned into a carbon template in pyrolysis to inhibit the aggregation of metal particles and confined them in mesoporous channels of KIT-6. The as-prepared CoxCu1/KIT-6 catalysts with different Co/Cu ratios (x=1-4) under high total metal loading (30 wt.%) were investigated. It is demonstrated that highly dispersed as well as uniformly distributed bimetallic Cu-Co active species were obtained in catalysts, which exhibited excellent performance for HAS even under high space velocity. The best performance went to Co3Cu1/KIT-6 catalyst with a CO conversion of 83.3% and a selectivity to C2+ alcohols of 59.8% under GHSV=9000 mL/gcat/h, and with no visible decrease in 200 h. Furthermore, combining TPR, XRD and chemisorption results, the surface area of Cu-Co alloy phase was quantitatively characterized. Correlated with the catalytic performance, a linear relationship between the space-time yield of C2+ alcohols and surface area of Cu-Co phase was established, which strongly confirmed the synergetic contribution of Cu-Co structure. The TOF was calculated as well. With the increase of copper contents, TOF decreased from 0.065 to 0.029 s-1. This may result from the inhibition of Cu addition to Co sites in C-O cleavage, leading to a loss of CO conversion. This method of effectively encapsulating CoCu species in ordered structure and the discussion of structure-activity relationship may provide more guidance for further design and fabrication of high-performance bimetallic catalysts.

High-performance CoCu catalyst encapsulated in KIT-6 for higher alcohol synthesis from syngas

2019 Spring National Meeting

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