【Frontiers in HaiChuan Chemical Technology】Research by the Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences, and others addresses the selectivity challenges in producing high-carbon oxygen compounds from syngas

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Direct conversion of syngas into higher oxygenated compounds presents numerous challenges; it is difficult to achieve a high CO conversion rate under mild reaction conditions, excellent selectivity for alcohols and other higher oxygenated compounds (ROH), as well as low levels of C1 by-products such as CO2 and CH4. Recently, a research team led by Fang Kegong from the Shanxi Coal Chemistry Institute of the Chinese Academy of Sciences and Sun Yuhan from the Shanxi Research Institute of the Huairou Laboratory developed a CuxPd1/SiO₂|CoMn multifunctional catalyst. By precisely controlling the spatial arrangement of active sites and the migration paths of intermediates, this team succeeded in overcoming this fundamental challenge. The optimized Cu28Pd1/SiO₂|CoMn catalyst achieved a one-way conversion rate of 27.3% for CO under mild reaction conditions, a molar selectivity of 44.4% for ROH, and a content of high-carbon alcohols of C2+ or higher at 95.4%; the selectivities for CO₂ and CH4 were reduced to 6.4% and 5.7%, respectively. Converting syngas directly into higher alcohol-containing oxygen compounds (C₂+OH, alcohols or aldehydes) holds significant market value. However, this reaction pathway is extremely complex, involving H₂/CO activation, C-C coupling, and water-gas shift reactions, and it presents numerous technical challenges; it is difficult to achieve a high CO conversion rate under mild reaction conditions, excellent selectivity for higher alcohol-containing oxygen compounds (ROH), and low levels of C1 by-products such as CO₂ and CH₄. Although the use of catalyst designs with dual active sites and tandem catalysts has improved the selectivity for ROH to a certain extent, there remain drawbacks such as low CO conversion rates under mild reaction conditions and the formation of large amounts of C1 by-products. It is therefore necessary to further develop new catalysts for the production of advanced alcohol-containing oxides from syngas, which exhibit excellent activity and ROH selectivity under mild reaction conditions, along with high carbon efficiency. The team developed a synthesized CuxPd1/SiO₂|CoMn multifunctional catalyst, which achieves excellent reaction performance featuring high CO conversion and ROH selectivity as well as low formation of C1 by-products, through a spatial decoupling process mediated by hydrogen spillover; the catalyst features a PdCu single-atom alloy structure and a Co0-Co₂C dual-active-site structure. The hydrogen overflow effect of PdCu single-atom alloys promotes the activation of H2 and the formation of CO2 hydrogenation products, increases the conversion rate of CO and the selectivity for ROH, suppresses the formation of CO2 and CH4, and raises the content of alcohols with C5+ structure. It is understood that this new development in research has clarified the catalytic mechanism for the direct conversion of syngas into higher oxygenated alcohols. Researcher Fang Kegong from the Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences, explained that during the reaction process, surface species of CHxO* (oxygen-containing hydrocarbon groups) generated by the PdCu single-atom alloy migrate to the Co0-Co2C interface, where they combine with the abundant CHx* (hydrocarbon-active group species) on that surface; further hydrogenation then leads to the formation of C2+ higher oxygenated alcohols. The study clearly demonstrates that on the surface of such catalysts, two insertion mechanisms—CO*/CHxO* (oxygenated hydrocarbon groups)—exist simultaneously within the syngas conversion reaction network. Moreover, the insertion barrier for CHxO* is lower, which facilitates the selective synthesis of higher alcohol-containing oxidized compounds and further suppresses the formation of C1 by-products.