The mechanism of higher alcohol formation on ZrO2-based catalyst from syngas

Renewable Butanol Production via Catalytic Routes

Fluctuating crude oil price and global environmental problems such as global warming and climate change lead to growing demand for the production of renewable chemicals as petrochemical substitutes. Butanol is a nonpolar alcohol that is used in a large variety of consumer products and as an important industrial intermediate. Thus, the production of butanol from renewable resources (e.g., biomass and organic waste) has gained a great deal of attention from researchers. Although typical renewable butanol is produced via a fermentative route (i.e., acetone-butanol-ethanol (ABE) fermentation of biomass-derived sugars), the fermentative butanol production has disadvantages such as a low yield of butanol and the formation of byproducts, such as acetone and ethanol. To avoid the drawbacks, the production of renewable butanol via non-fermentative catalytic routes has been recently proposed. This review is aimed at providing an overview on three different emerging and promising catalytic routes from biomass/organic waste-derived chemicals to butanol. The first route involves the conversion of ethanol into butanol over metal and oxide catalysts. Volatile fatty acid can be a raw chemical for the production of butanol using porous materials and metal catalysts. In addition, biomass-derived syngas can be transformed to butanol on non-noble metal catalysts promoted by alkali metals. The prospect of catalytic renewable butanol production is also discussed.

Role of Ga3+ promoter in the direct synthesis of iso-butanol via syngas over a K–ZnO/ZnCr2O4 catalyst

ZG, gallium cluster and ZnGa₂O₄ were formed by introducing Ga³⁺ to K–ZnO/ZnCr₂O₄ iso-butanol catalyst. Only a moderate amount of ZG promotes the space time yield (STY) and selectivity of alcohols for iso-butanol synthesis.

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.

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.