Chem Soc Rev Front Cover Article: New horizon in C1 chemistry: breaking the selectivity limitation in transformation of syngas and hydrogenation of CO2 into hydrocarbon chemicals and fuels

Article Link: https://pubs.rsc.org/en/content/articlelanding/2019/cs/c8cs00502h#!divAbstract

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X-MoL报道: https://www.x-mol.com/news/17564

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Our review article on catalytic conversion of syngas and CO₂ to liquid fuels and chemicals has been published in Chemical Society Reviews and has been chosen as the Front Cover of Issue No. 12 of Vol. 48 of Chemical Society Reviews.

Catalytic transformations of syngas (a mixture of H₂ and CO), which is one of the most important C1-chemistry platforms, and CO₂, a greenhouse gas released from human industrial activities but also a candidate of abundant carbon feedstock, into chemicals and fuels have attracted much attention in recent years. Fischer–Tropsch (FT) synthesis is a classic route of syngas chemistry, but the product selectivity of FT synthesis is limited by the Anderson–Schulz–Flory (ASF) distribution. The hydrogenation of CO₂ into C₂₊ hydrocarbons involving C–C bond formation encounters similar selectivity limitation. Selectivity control is the biggest challenge in syngas and CO₂ conversions.

Recently, significant breakthroughs have been achieved on hydrogenation of both CO and CO₂ into liquid fuels, olefins and aromatics via using the reaction coupling strategy. The selectivity of products breaks the limitation by the ASF distribution. The present article systemically reviews recent advances in the design and development of novel bifunctional or multifunctional catalysts for hydrogenation of CO and CO2 into C₂₊ hydrocarbons including liquid fuels (gasoline C₅-C₁₁, jet fuel C₈-C₁₆ and diesel fuel C₁₀-C₂₀) and chemicals (C₂-C₄ olefins and aromatics). The key factors in controlling the catalytic performance, the reaction mechanism, in particular the activation of CO and CO₂, the reaction pathway and the reaction intermediate, have be discussed to provide a deep understanding of the chemistry of the new C1 chemistry routes beyond FT synthesis.

This review article mainly involves two types of bifunctional catalysts. The first type of catalysts is composed of FT catalysts and zeolites. FT catalysts, such as Fe (Fe_xC_y), Co and Ru, are responsible for the activation of CO and the growth of carbon chain. Zeolites are in charge of the hydrocracking/isomerisation or hydrogenolysis. High selectivity of middle-distillate liquid fuels, such as gasoline (C₅-C₁₁ hydrocarbons), jet fuel (C₈-C₁₆ hydrocarbons) and diesel fuel (C₁₀-C₂₀ hydrocarbons), have been obtained over such kind of bifunctional catalysts. The effect of topology, acidity and mesoporosity of zeolites as well as the sizes of metal nanoparticles and support mesopores on product selectivity has been discussed. The importance of hydrocracking on acid sites and hydrogenolysis on the metal nanoparticles for the selective C-C cleavage has also been analyzed.

The second type of catalysts is composed of metal oxides (such as the solution solid ZnO-ZrO₂, In₂O₃-ZrO₂ and the spinel structure of ZnCr₂O₄, ZnAl₂O₄, ZnGa₂O₄) and zeolites (such as SAPO-34, ZSM-5, MOR). The activation of CO to intermediates (CH₃OH/DME or ketene) proceed on the metal oxides and the selective C-C bond formation proceed on the zeolites. The reaction mechanism of such kind of bifunctional catalysts differs from that of the conventional FT catalysts, which represents a new route for the catalytic conversion of CO and CO₂. The selectivity of lower olefins and aromatics could reach 80% over these bifunctional catalysts. The key factor influencing the product selectivity such as the acidity of the zeolite and the proximity between the two components has been discussed. The reaction pathway, kinetic studies, reaction mechanism have also been deeply analyzed. The conclusion section ont only summarizes the major advantages and disadvantages of the bifucntional catalysts but also offers prospects for the design of new C1 chemistry systems by using the concept of bifunctional catalysis or tandem catalysis.