Regulating Oxygen Vacancies for Enhanced Higher Oxygenate Synthesis via Syngas

Constructing highly efficient dual active sites for preferential formation of higher oxygenates via direct syngas conversion remains a grand challenge. Herein, we reported that the regulation of oxygen vacancy density of metal–oxide support could effectively promote the production of oxygenates. Compared with an inert SiO2-supported Co-based catalyst, the rutile TiO2-supported catalyst with abundant oxygen vacancies exhibited up to 44.7% CO conversion with the selectivity and space–time yield (STY) of the oxygenate increased to 43.4 wt % and 50 mg gcat.–1 h–1, respectively. Further studies established a nearly linear relationship between the density of the oxygen vacancy and the atomic ratio of Co2+/Co0 or the STY of oxygenated products. Characterization confirmed that the oxygen vacancies not only promote CO adsorption, dissociation, and subsequently the carburization of cobalt species to form Co2C but also create a C-rich and H-poor local microchemical environment that benefits CO associative adsorption and CO bond insertion to form oxygenates. The synergistic effect of oxygen vacancies and the Co0/Co2C interface site contributed to the observed enhanced performance for direct syngas conversion to higher oxygenates

Advances in Selectivity Control for Fischer–Tropsch Synthesis to Fuels and Chemicals with High Carbon Efficiency

Fischer–Tropsch synthesis (FTS) is a versatile technology to produce high-quality fuels and key building-block chemicals from syngas derived from nonpetroleum carbon resources such as coal, natural gas, shale gas, biomass, solid waste, and even CO2. However, the product selectivity of FTS is always limited by the Anderson–Schulz–Flory (ASF) distribution, and the key scientific problems including selectivity control, energy saving, and CO2 emission reduction still challenge the current FTS technology. Herein, we review recent significant progress in the field of FTS to obtain specific target products including fuels, olefins, aromatics, and higher alcohols with high selectivity. These achievements are enabled by developing highly efficient catalysts and a controlled reaction pathway based on an integrated process. The structural nature of catalytic active sites and established structure–performance relationships are clarified. Moreover, we specially focus on the carbon utilization efficiency, and the efforts to tune the preferential formation of value-added chemicals and strategies to reduce CO2 selectivity are summarized. The challenges and the perspectives for future FTS technology development with high carbon efficiency are also discussed

characterizationofcomncatalystbyinsituxrayabsorptionspectroscopyandwaveletanalysisforfischertropschtoolefinsreaction

Cobalt carbide has recently been reported to catalyse the FTO con version of syngas with high selectivity for the production of lower olefins (C2-C4). Clarifying the formation process and atomic structure of cobalt carbide will help understand the catalytic mechanism of FTO. Herein, hydrogenati on of carb on monoxide was investigated for cobalt carbide synthesized from CoMn catalyst, followed by X-ray diffraction, transmission electron microscopy, temperature programmed reaction and in situ X-ray absorption spectroscopy. By monitoring the evolution of cobalt carbide during syngas conversion, the wavelet transform results give evidenee for the formation of the cobalt carbide and clearly demonstrate that the active site of catalysis was cobalt carbide

Controlled Fabrication of Iron Oxide/Mesoporous Silica Core–Shell Nanostructures

A simple and reproducible method for the preparation of well-defined iron oxide/mesoporous silica core–shell nanostructure is provided. Iron oxide nanocubes with a narrow size distribution were synthesized through a novel ethanol/acetic acid system using Fe­(NO₃)·9H₂O as an iron source and polyvinylpyrrolidone as a capping agent under mild solvothermal conditions (200 °C). These monodisperse nanoparticles were used directly as the core for the deposition of a mesoporous silica shell via a sol–gel process, resulting in uniform core–shell Fe₂O₃@SiO₂ composites with tailored silica shell thickness and controllable core morphology. In addition, composition as well as magnetization of the reduced core–shell composites could easily be controlled by a reduction process. Furthermore, the iron oxide core in Fe₂O₃@SiO₂ could be completely etched to produce hollow SiO₂ nanospheres. The mechanism of formation of the core–shell structure was also proposed by the aid of IR spectrum analysis

Mechanism of the Mn Promoter via CoMn Spinel for Morphology Control: Formation of Co₂C Nanoprisms for Fischer–Tropsch to Olefins Reaction

The Fischer–Tropsch to olefins (FTO) reaction over Co₂C catalysts is structure-sensitive, as the catalytic performance is strongly influenced by the surface structure of the active phase. The exposed facets determine the surface structure, and it remains a great challenge to precisely control the particle morphology of the FTO active phase. In this study, the controlling effect of the Mn promoter on the final morphology of the Co₂C nanoparticles for the FTO reaction was investigated. The unpromoted catalyst and several promoted catalysts with Ce, La, and Al were also studied for comparison. For the Mn-promoted catalysts, the combination method of the Co and Mn components plays a crucial role in the final morphology of Co₂C and thus the catalytic performance. For the CoMn catalyst prepared by coprecipitation, Co₂C nanoprisms with specifically exposed facets of (101) and (020) can be obtained, which exhibit a promising FTO catalytic performance with high C_2–4⁼ selectivity, low methane selectivity, and high activity under mild reaction conditions. However, for the Mn/Co catalyst prepared via impregnation, Co₂C nanospheres are formed, which exhibit high methane selectivity, low C_2–4⁼ selectivity, and low activity. For the unpromoted catalyst and the catalysts promoted by Ce and La, Co₂C nanospheres are also obtained, with catalytic performance similar to that of the Mn/Co catalyst prepared via impregnation. Due to the high stability of the Co₂AlO_<i>x</i> composite oxide, no Co₂C phase can be formed for the catalyst promoted by Al