Direct Production of Value-Added Chemicals Via Syngas Conversion

Syngas conversion to fuels and chemicals is one of the most challenging subjects in the field of C1 chemistry. It is considered as an attractive alternative non-petroleum-based production route. The direct synthesis of high value-added olefins and alcohols from syngas has drawn particular attention due to due to its process simplicity, low energy consumption and clean utilization of carbon resource. Fischer-Tropsch synthesis (FTS) is a heterogeneous catalytic process for sustainable production of fuel and value-added chemicals via syngas. It is a very complicated catalytic reaction process with co-production of paraffin, olefin, alcohol and other products. The product selectivity is controlled by many factors, such as catalyst systems, reactors and operation conditions. For the purpose of high selectivity to specific value-added olefins or alcohols, it is very desirable to regulate the reaction network for certain reactions to take place preferentially. Obviously, it is necessary to control CO activation and then both carbon chain growth and termination for high selectivity to target product by development new catalyst systems and optimization of reaction conditions.

Fischer-Tropsch to olefins by using new active phase was firstly investigated. Co₂C nanoprisms with exposed facet of {101} and {020} were prepared and tested for syngas conversion. High selectivity for the production of lower olefins (60.8 C%) was achieved, while little methane (about 5.0 C%) was generated with the ratio of olefin/paraffin amongst the C_2-4 products being as high as 30. The product distribution deviates markedly from the classical ASF distribution with the highest selectivity to propylene. The effect of reaction conditions and various promoters, structure-performance relationship, and the model for modified ASF distribution were discussed.

Higher alcohol synthesis by dual active sites was also investigated. Several kinds of dual active sites (Cu/FeC_x, CuCo, and Co/Co₂C) were tested for higher alcohol synthesis. Both Cu/FeC_x and Co/Co₂C could afford high selectivity for long chain alcohols, while only short chain alcohols were produced for CuCo. The difference of the detailed surface structure and the corresponding catalytic performance was studied in detail.