Formation Of Cobalt Carbide Research Articles

Performance of Co-Fe@Alumina catalysts in comparison to monometallic Co@Alumina and Fe@Alumina catalysts for microwave assisted COx-free hydrogen production

Alumina supported mono and bimetallic Co and Fe catalysts, with different metal loading and different Co/Fe ratio, were used for decomposition reaction of ammonia to produce COx-free hydrogen in the microwave reactor system by mixing with mesoporous carbon. The structural and surface properties of the catalysts before and after being exposed to microwave radiation at the catalytic bed were examined by different techniques. Catalysts exhibited high catalytic performance in the microwave system, such that total conversion was achieved at 400 °C under the flow of ammonia (GHSV of 36,000 ml/gcat.h), while they showed negligible activity in the conventionally heated reactor system. Microwave exposure causes the formation of cobalt carbide and iron carbide in the structure of monometallic cobalt and monometallic iron catalysts, respectively. Moreover a phase transition from γ-alumina toα -alumina was recognized for both of them. Long term exposure to microwave further enhance the carbide formation that could be effective getting stable conversion values in time on stream experiments. While, alumina supported monometallic cobalt catalysts gave better yield than alumina supported monometallic iron catalysts in both of the systems, bimetallic catalysts showed better activity than monometallic catalysts, especially at temperatures lower than 400 °C.

Polyol Synthesis of Cobalt–Copper Alloy Catalysts for Higher Alcohol Synthesis from Syngas

Novel catalysts for the selective production of higher alcohols from syngas could offer improved pathways towards synthetic fuels and chemicals. Cobalt–copper alloy catalysts have shown promising results for this reaction. To improve control over particle properties, a liquid phase nanoparticle synthesis based on the polyol method was selected to synthesize Co2.5Cu particles, which were then supported onto a variety of metal oxide supports (Al2O3, SiO2, TiO2, ZrO2). The catalysts were characterized by transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy before and after catalytic testing in a flow reactor at 250 °C and 40 bar. The results show alloyed phases were obtained using the polyol method, resulting in selectivity towards higher alcohols, as high as 11.3% when supported on alumina. Segregation of cobalt and the formation of cobalt carbide were observed in the catalysts after catalytic testing, which may limit performance compared to the desired alloy phase.

Preparation and characterization of lanthanum-promoted cobalt–copper catalysts for the conversion of syngas to higher oxygenates: Formation of cobalt carbide

A series of La-promoted cobalt–copper catalysts with various Co:Cu ratios have been used to study the conversion of syngas to oxygenates and hydrocarbons. In particular, the effect of the Co:Cu composition on the selectivity to oxygenates versus hydrocarbons has been examined.Three bulk catalysts were synthesized by coprecipitation, reduced in H2/He flow, and then cobalt carbide was formed during CO hydrogenation. The composition of the catalysts was as follows: Cu:Co=12:9, 7:13, and 0:21 (cobalt only). CO hydrogenation tests were performed at differential conversions and 30bar, H2/CO=2/1 and 250°C.The C1 selectivity (methane+methanol+CO2) was ∼64% for the two catalysts containing Co and Cu, and slightly less for the Co-only catalyst (52%). These products are formed by three mechanisms: (1) CH4: hydrogenation of dissociatively adsorbed CO at metallic cobalt sites, (2) CH3OH: hydrogenation of associatively adsorbed CO at copper sites, and (3) CO2: water gas shift, also at the copper sites. C2+ alcohol selectivity for the two Cu-containing catalysts is greater than for the Co-only catalyst, while the Co-only catalyst has the highest selectivity to acetaldehyde. The formation of C2+ oxygenates is consistent with the CO insertion mechanism, in which associatively adsorbed CO is inserted into the CHx species and forms the first C–C bond, producing a CHxCO intermediate that can be hydrogenated into ethanol or acetaldehyde.

Insitu magnetometer study on the formation and stability of cobalt carbide in Fischer–Tropsch synthesis

While carbides are always present in iron-based Fischer–Tropsch synthesis, very little is known about the presence and the role of carbides in cobalt-based CO hydrogenation. Cobalt carbide, Co2C, has been reported in catalysts where operational upsets occurred and it is associated with low catalyst activity and increased methane selectivity. In this study, a novel insitu magnetometer was used to study the formation and the stability of cobalt carbide during the Fischer–Tropsch synthesis at fully relevant conditions. The formation of cobalt carbide was confirmed by means of insitu XRD and synchrotron XRD measurements. Cobalt carbide is relatively stable at typical reaction conditions, but a rapid decomposition into hcp cobalt occurs in hydrogen above 150°C. Cobalt carbide formation is inversely proportional to the H2/CO ratio and the reaction temperature. However, the amounts of cobalt carbide formed are small and the impact on deactivation at realistic Fischer–Tropsch conditions should generally be negligible.

Study on the effect of alkali promoters on the formation of cobalt carbide (Co2C) and on the performance of Co2C via CO hydrogenation reaction

The present investigation deals with an alkali metal assisted synthesis of cobalt carbide (Co2C), starting from carburizing reduced complex precursors (obtained from Co3O4 with the addition of Li2O, Na2O and K2O) using CO as a carburization source. It is found that the Co2C formation could be significantly accelerated by the Li component. A comparative study reveals that the promotion effect of Li component may be related to the H2 adsorption on the reduced precursor, which enhanced the ability of the precursor to react with CO. Furthermore, the Co2C prepared from the precursor containing Li component shows a considerable increase in activity for CO hydrogenation and an improved fraction of higher alcohols in the total alcohol products, compared to the Co2C prepared without promoters. An attempt is made to elucidate the catalytic behavior of the as-prepared Co2C samples.

Effect of the Reduction Temperature of Co-La-Zr/AC on the Synthesis of Higher Alcohols from Syngas

CO hydrogenation over a Co-La-Zr/AC catalyst prepared by co-impregnation and reduced at different temperatures was studied. The catalyst reduced at 703 K showed good activity at 3.0 MPa, 495 K, H2/CO (V/V) = 2, and GHSV = 500h−1. CO conversion and selectivity for total alcohols were 59.1% and 42.0%, respectively, and C6–C18 higher alcohols were 50.4% of the alcohols. Metallic cobalt and cobalt carbide were detected by XRD as the main cobalt species. The reduction temperature affects both the cobalt dispersion and formation of cobalt carbide. Cobalt carbide may play an important role in the synthesis of higher alcohols on Co-La-Zr/AC.

Role of the Cu–Co alloy and cobalt carbide in higher alcohol synthesis

Formation and decomposition of the Cu–Co alloy and Co 2C were studied using in situ X-ray diffraction (XRD), TG-DTA and TEM techniques. Cu–Co alloy with ratio Cu/Co=1:1 has been obtained under treatment of CuCoO 2 with hydrogen at 230–300°C. Co 2C was formed from Cu–Co alloy at 280–310°C and decomposed at 390–400°C under CO. It was shown that the role of Cu–Co alloy consisted in formation of cobalt carbide was able to activate CO undissociatively that led to oxygenates synthesis.