Status and prospects in higher alcohols synthesis from syngas

Higher alcohols are important compounds with widespread applications in the chemical, pharmaceutical and energy sectors. Currently, they are mainly produced by sugar fermentation (ethanol and isobutanol) or hydration of petroleum-derived alkenes (heavier alcohols), but their direct synthesis from syngas (CO + H₂) would comprise a more environmentally-friendly, versatile and economical alternative. Research efforts in this reaction, initiated in the 1930s, have fluctuated along with the oil price and have considerably increased in the last decade due to the interest to exploit shale gas and renewable resources to obtain the gaseous feedstock. Nevertheless, no catalytic system reported to date has performed sufficiently well to justify an industrial implementation. Since the design of an efficient catalyst would strongly benefit from the establishment of synthesis-structure-function relationships and a deeper understanding of the reaction mechanism, this review comprehensively overviews syngas-based higher alcohols synthesis in three main sections, highlighting the advances recently made and the challenges that remain open and stimulate upcoming research activities. The first part critically summarises the formulations and methods applied in the preparation of the four main classes of materials, i.e., Rh-based, Mo-based, modified Fischer-Tropsch and modified methanol synthesis catalysts. The second overviews the molecular-level insights derived from microkinetic and theoretical studies, drawing links to the mechanisms of Fischer-Tropsch and methanol syntheses. Finally, concepts proposed to improve the efficiency of reactors and separation units as well as to utilise CO₂ and recycle side-products in the process are described in the third section.

Binary ZnO/Zn–Cr nanospinel catalysts prepared by a hydrothermal method for isobutanol synthesis from syngas

A series of binary ZnO/Zn–Cr nanospinel catalysts were prepared by a hydrothermal method and applied in direct synthesis of isobutanol from syngas, during which the effect of the hydrothermal time/temperature on their catalytic performance in the isobutanol synthesis has been investigated at 400 °C and 10 MPa.

The role of non-stoichiometric spinel for iso-butanol formation from biomass syngas over Zn–Cr based catalysts

The non-stoichiometric Zn–Cr spinel plays an essential role for the formation of iso-butanol from bio-syngas. Co-precipitation method promotes the formation of non-stoichiometric Zn–Cr spinel and dramatically enhances the catalytic performance.

The role of potassium promoter in isobutanol synthesis over Zn–Cr based catalysts

The potassium promoter would tailor the microstructure of the Zn–Cr spinel and stabilize the surface hydroxyl species which greatly facilitate the formate of isobutanol.

The real active sites over Zn–Cr catalysts for direct synthesis of isobutanol from syngas: structure-activity relationship

The isobutanol productivity is closely related to the cation disorder distribution.

Application of spinel-type cobalt chromite as a novel catalyst for combustion of chlorinated organic pollutants

Various chromium-containing catalysts were tested for the total oxidation of trichloroethylene (TCE) as a model reaction for the catalytic combustion of chlorinated organic pollutants. A spinel-type cobalt chromite (CoCr2O4) among others was proven to be a very promising catalyst showing higher activity and higher CO2 selectivity than traditional alumina supported chromia. Even if both Cr3+ and Cr6+ species were observed on the surface of CoCr2O4, the Cr6+ species was stable under reducing environment. The presence of Cr3+-Cr6+ pair sites and the effect of redox treatments on the activity were investigated to explain the nature of possible active sites for TCE decomposition. Higher selectivity to CO2 of CoCr2O4 was ascribed to the abundance of its Cr3+ species, together with its activity for water gas shift reaction.