Cobalt carbide nanoprisms for direct production of lower olefins from syngas

Abstract

Lower olefins-generally referring to ethylene, propylene and butylene-are basic carbon-based building blocks that are widely used in the chemical industry, and are traditionally produced through thermal or catalytic cracking of a range of hydrocarbon feedstocks, such as naphtha, gas oil, condensates and light alkanes. With the rapid depletion of the limited petroleum reserves that serve as the source of these hydrocarbons, there is an urgent need for processes that can produce lower olefins from alternative feedstocks. The 'Fischer-Tropsch to olefins' (FTO) process has long offered a way of producing lower olefins directly from syngas-a mixture of hydrogen and carbon monoxide that is readily derived from coal, biomass and natural gas. But the hydrocarbons obtained with the FTO process typically follow the so-called Anderson-Schulz-Flory distribution, which is characterized by a maximum C-C hydrocarbon fraction of about 56.7 per cent and an undesired methane fraction of about 29.2 per cent (refs 1, 10, 11, 12). Here we show that, under mild reaction conditions, cobalt carbide quadrangular nanoprisms catalyse the FTO conversion of syngas with high selectivity for the production of lower olefins (constituting around 60.8 per cent of the carbon products), while generating little methane (about 5.0 per cent), with the ratio of desired unsaturated hydrocarbons to less valuable saturated hydrocarbons amongst the C-C products being as high as 30. Detailed catalyst characterization during the initial reaction stage and theoretical calculations indicate that preferentially exposed {101} and {020} facets play a pivotal role during syngas conversion, in that they favour olefin production and inhibit methane formation, and thereby render cobalt carbide nanoprisms a promising new catalyst system for directly converting syngas into lower olefins.

Directly converting CO2 into a gasoline fuel

“…Typically, iron catalysts need alkali metal promotion to attain desired activity and selectivity. It was reported that the addition of Na is beneficial to olefin production222324. The existence of Na obviously enhances the surface basicity and carburization of iron-based catalyst, making the catalyst very active for CO 2 hydrogenation to light olefins14.…”

Chemical imaging of Fischer-Tropsch catalysts under operating conditions

“…However, only in the past few years has the understanding of the physicochemical signatures of an active Co FTS catalyst developed ( 13 , 14 ). This new understanding has evolved mainly as a result of detailed studies of well-defined model catalysts, often investigated using novel x-ray–based catalyst characterization techniques ( 15 ).…”

Metal organic framework-mediated synthesis of potassium-promoted cobalt-based catalysts for higher oxygenates synthesis

“…Alkali metals, including K, Na and Li [24,26,50], are reported to promote Co 2 C formation in CO hydrogenation reactions. Thus, the formation of cobalt carbide is enhanced in these K-promoted catalysts, and these catalysts had higher selectivity to oxygenates, especially for the catalysts with high potassium composition.…”

“…Therefore, the catalyst favors carbon chain polymerization rather than CO insertion [20]. Recently, several studies on cobalt-based FischerTropsch catalysts or higher alcohol synthesis catalysts have reported the formation of cobalt carbide in the presence of syngas [20][21][22][23][24][25][26]. Pei et al [23] and Bian et al [27] claim that cobalt carbide (Co 2 C) can adsorb CO nondissociatively, and insert the CO to adjacent C x H y species.…”