Novel cobalt zinc oxide Fischer-Tropsch catalysts synthesised using supercritical anti-solvent precipitation

Cobalt zinc oxide catalysts have been prepared by anti-solvent precipitation in supercritical CO2 and investigated for CO hydrogenation. Here we show how the textural and catalytic properties of the catalyst can be tailored by the addition of water to the initial solution of cobalt and zinc acetates in methanol. Characterization of the catalysts by powder X-ray diffraction, infra-red and Raman spectroscopy showed that in the absence of water a high surface area mixed acetate was produced which upon calcination formed wurtzite type Zn1−xCoxO and spinel type ZnxCo3−xO4. The addition of 5 vol.% water resulted in a phase separated Co3O4/ZnO catalyst and enhanced active cobalt surface area as a result of disruption of the solvent/CO2 phase equilibrium during precipitation

Green preparation of transition metal oxide catalysts using supercritical CO2 anti-solvent precipitation for the total oxidation of propane

A series of metal oxide catalysts, including Fe3O4, NiO, CuO and Co3O4, have been prepared by supercritical anti-solvent precipitation and evaluated for the total oxidation of propane. Co3O4 was found to be the most active catalyst and our studies have focussed on this oxide. The addition of water as co-solvent in the supercritical anti-solvent preparation was investigated. Powder X-ray diffraction and infrared spectroscopy indicated that the addition of water promoted the formation of carbonate species in the catalyst precursors. The formation of the catalysts from the precursor were optimised by investigating the thermal treatment conditions, by studying variables including time, temperature and atmosphere. The optimal conditions for catalyst preparation required precursor precipitation containing 10 vol% water co-solvent followed by a 2 h calcination at 250 °C. These conditions produced Co3O4 with high surface areas (>100 m2 g−1), which were very active catalysts producing 50% propane conversion at 175 °C

Green preparation of transition metal oxide catalysts using supercritical CO2 anti-solvent precipitation for the total oxidation of propane

A series of metal oxide catalysts, including Fe3O4, NiO, CuO and Co3O4, have been prepared by supercritical anti-solvent precipitation and evaluated for the total oxidation of propane. Co3O4 was found to be the most active catalyst and our studies have focussed on this oxide. The addition of water as co-solvent in the supercritical anti-solvent preparation was investigated. Powder X-ray diffraction and infrared spectroscopy indicated that the addition of water promoted the formation of carbonate species in the catalyst precursors. The formation of the catalysts from the precursor were optimised by investigating the thermal treatment conditions, by studying variables including time, temperature and atmosphere. The optimal conditions for catalyst preparation required precursor precipitation containing 10 vol% water co-solvent followed by a 2 h calcination at 250 °C. These conditions produced Co3O4 with high surface areas (>100 m2 g−1), which were very active catalysts producing 50% propane conversion at 175 °C

Supercritical antisolvent precipitation of TiO2 with tailored anatase/rutile composition for applications in redox catalysis and Ppotocatalysis

TiO2 with tailored anatase/rutile composition has been prepared from the supercritical antisolvent (SAS) precipitation of a range of titanium alkoxides. The calcination of the SAS TiO2 was monitored by in situ powder X-ray diffraction to determine the optimal calcination conditions for the formation of a mixed anatse/rutile phase TiO2. The SAS precipitated material calcined at 450 °C produced a predominantly anatase support while calcination at 750 °C resulted in a 90 wt% anatase and 10 wt% rutile TiO2. 5 wt% AuPd was added to the SAS TiO2 using an impregnation technique, with exceptional dispersion of the metals being observed by transmission electron microscopy. Mean metal particle sizes were determined to be below 1 nm for both anatase and anatase/rutile SAS TiO2 materials. These catalysts were found to be highly active for the selective oxidation of benzyl alcohol and the direct synthesis of hydrogen peroxide. In addition the anatase/rutile SAS TiO2 was found to have comparable activity to commercial anatase/rutile mixed phase TiO2 for the photocatalytic splitting of water for hydrogen production

Preparation of Fischer–Tropsch Supported Cobalt Catalysts Using a New Gas Anti-Solvent Process

Cobalt and ruthenium-promoted cobalt Fischer–Tropsch catalysts supported on titania have been prepared for the first time by gas anti-solvent precipitation. The use of dense CO₂ as an anti-solvent enables the precipitation of cobalt acetate and ruthenium acetylacetonate onto preformed titania. The gas anti-solvent process produces catalysts with the desired 20 wt % cobalt content as precursors, which on calcination give highly dispersed Co₃O₄. The addition of ruthenium to the gas anti-solvent prepared cobalt catalysts has been investigated by two methods (a) coprecipitation with cobalt acetate and (b) wet impregnation onto a precalcined cobalt titania catalyst, and these resulted in catalysts with distinctly different properties. These catalysts were compared with a standard ruthenium-promoted cobalt catalyst prepared by wet impregnation and were found to be substantially more active for the Fischer–Tropsch reaction