Search

A series of alkali metal (Li, Na, K, Rb and Cs) doped Ru/AC catalysts were prepared and were investigated for the acetylene hydrochlorination. The results showed a relationship between the catalytic activity and K loading, 0.5Ru0.5 K/AC catalyst exhibited the highest acetylene conversion of 71.6% and vinyl chloride monomer productivity of 194 kgvcmkgRu−1 h−1 under 180 °C and C2H2 hourly space velocity (GHSV) of 180 h−1. The characterization results revealed that the addition of K promoted the dispersion of Ru species and inhibited the coke deposition. In addition, the VCM productivity increased with the atomic number of the alkali metal.

Cu/Zn/Al/Zr catalysts with Cu2+:Zn2+:Al3+:Zr4+ = 2:1:x:0.1 (x = 0.6–1.5) were prepared from hydrotalcite-like precursors by co-precipitation method and tested for the CO2 hydrogenation to methanol. Both Cu/Zn/Al/Zr hydrotalcite-like and malachite phase were formed at low Al content. However, with the increase of Al content, the yield of hydrotalcite-like phase increased and phase-pure Cu/Zn/Al/Zr hydrotalcite-like compound was obtained for x ≥ 0.9. In addition, both the specific surface area and the dispersion of Cu increased gradually with the increase of Al, while the exposed Cu surface area first increased until Al content was 27.9 mol%, then decreased. The results of catalytic test for CO2 hydrogenation revealed that Cu/Zn/Al/Zr catalysts via phase-pure hydrotalcite-like compounds exhibited much better catalytic performance with higher CO2 conversion and CH3OH selectivity compared with the catalyst derived from mixed phase (hydrotalcite-like and malachite). The Cu/Zn/Al/Zr catalysts with Cu2+:Zn2+:Al3+:Zr4+ = 2:1:1.2:0.1 resulting from phase-pure hydrotalcite-like precursors afforded the substantial stability and the best catalytic performance.

Following our previous findings that spatial confinement using core@shell cobalt-based catalysts could regulate the product distribution toward desired distillate. We developed a facile solvothermal method to prepare Co 3 O 4 @C-mesoporous SiO 2 (Co 3 O 4 @C- m -SiO 2 ) catalysts with inert C modified surface of mesoporous channel using PVP polymer as carbon source. High-resolution transmission electron microscopy (HRTEM) characterization result, together with the N 2 physisorption, indicated that the Co 3 O 4 @C- m -SiO 2 catalysts with inert C modified mesoporous channel could be prepared via carbonization of PVP polymer under argon gas instead of calcination and mesoporous silica shell could also be fabricated after inert C modification, and thus higher mesoporous nature contributed to the facile access of the reactant gas to the active Co sites and diffusion of formed product. Hydrogen temperature programmed reduction (H 2 -TPR) showed that the degree of reduction for the Co 3 O 4 @C- m -SiO 2 catalysts were enhanced gradually with increase of C modifier content due to weak Co–C interaction instead of strong Co-silica interaction in the Co 3 O 4 @ m -SiO 2 catalysts. As a result, such inert C modified cobalt-based catalyst with core@shell structure, which possessed rigid porous framework to allow free access of syngas and inhibit mesoporous channel collapsing during F–T reaction, showed the higher catalytic activity and stability due to synergetic effect between higher Co dispersion and reducibility. Moreover, hydrophobic channel of the Co@C- m -SiO 2 catalysts with different C modifier content, which were likely favorable to the internal transportation of H 2 O byproduct and spatial confined effect for the formed hydrocarbon, led to a better selectivity toward C 5 –C 18 fraction than that of unmodified Co@ m -SiO 2 catalysts in the FTS.

Monodispersible Co3O4 nanoparticles were prepared via a facile solvothermal route using polyvinylpyrrolidone (PVP) as capping agent and the porous silica shell was then coated by means of the Stober process to fabricate Co3O4@porous-SiO2 (Co3O4@p-SiO2) nanocomposites. The particle size of Co3O4 and porous silica shell thickness of Co3O4@p-SiO2 nanocomposites could be easily controlled through changing the amount of PVP and tetraethoxysilane, respectively. The high resolution transmission electron microscopy results, together with the X-ray diffraction results, indicated that monodispersible Co3O4 nanoparticles were successfully prepared and uniformly encapsulated by porous silica. During the growth of silica shell, the PVP was trapped and dispersed in the silica shell. As a result, the porous silica shell was obtained after burning off the PVP and a positive correlation existed between the Brunauer–Emmett–Teller surface area of the porous silica shell and quantity of PVP in the original Co3O4 nanoparticles. Compared with the Co/SiO2 reference catalyst, CO conversion of the Co@p-SiO2 model catalyst was more stable and higher in a period of 240 h, and hydrocarbon selectivity towards C5–C18 fraction was also higher than that of the Co/SiO2 catalyst. The results of analysis for the Co@p-SiO2 catalyst showed that core@shell structure could maintain high dispersion of Co particles so as to provide higher number of Co active sites, and enhance selectivity towards C5–C18 fraction due to confined structure of porous channel in the silica shell. Schematic diagram of the procedure for synthesizing Co3O4@p-SiO2 nanocomposites.