Preparation and catalytic properties of transition metal carbides and nitrides

C2 to C4 olefins are traditionally produced from steam cracking of naphtha. The necessity for alternative production routes for these major commodity chemicals via non-oil-based processes has driven research in past times during the oil crises. Currently, there is a renewed interest in producing lower olefins from alternative feedstocks such as coal, natural gas, or biomass, in view of high oil prices, environmental regulations, and strategies to gain independence from oil imports. This review describes the major routes for the production of lower olefins from synthesis gas with an emphasis on a direct or single step process, the so-called FTO or Fischer–Tropsch to olefins process. The different catalysts for FTO are outlined and compared, and the key issues and requirements for future developments are highlighted. Iron-based catalysts are prevailing for FTO, and reproducible lower olefin selectivities of 50 wt % of hydrocarbons produced have been realized at CO conversions higher than 70% for 60 to 1000 ...

Catalysts for Production of Lower Olefins from Synthesis Gas: A Review

Carbide and Nitride Overlayers on Early Transition Metal Surfaces: Preparation, Characterization, and Reactivities.

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.

Status and prospects in higher alcohols synthesis from syngas

The carbides and nitrides of Mo and W can adsorb and activate hydrogen. The effects of particle size and surface area on the total amount of adsorbed hydrogen differ from those observed for transition metal sulfides. In the former case, this amount increases with increasing particle size and/or decreasing surface area. This is consistent with the involvement of the sub-surface regions of the crystallites during hydrogen adsorption. The activity for hydrogenation, hydrodesulfurization and hydrodenitrogenation exhibits similar trends. The high HDN activity of the Mo(W) carbide and nitride based catalysts has been noted. These catalysts are stable under typical hydroprocessing conditions although a partial sulfidation of their surface during HDS cannot be avoided.

Metal carbides and nitrides as potential catalysts for hydroprocessing

Preparation and benzene hydrogenation activity of supported molybdenum carbide catalysts

Mixed alcohol synthesis from carbon monoxide and dihydrogen over potassium-promoted molybdenum carbide catalysts

In the hydrogenation of CO at atmospheric pressure, unsupported molybdenum carbide catalyst produced mostly C1-C5 paraffins. Promotion of the catalyst with K2CO3 yielded C2-C5 hydrocarbons consisting of 80–100% olefins and reduced the methane selectivity. The selectivity of C2-C5 olefins among all hydrocarbon products was 50–70 wt% at CO conversions up to 70%.

Ki Yeop Park

Papers

Preparation and benzene hydrogenation activity of supported molybdenum carbide catalysts

Mixed alcohol synthesis from carbon monoxide and dihydrogen over potassium-promoted molybdenum carbide catalysts

Selective synthesis of light olefins from syngas over potassium-promoted molybdenum carbide catalysts