ABSTRACT
This paper deals with the textural, microstructural and interfacial properties of Au/TiO(2) nanocomposites, in relation to their photocatalytic activity for splitting of water. TiO(2) samples of two different morphologies were employed for dispersing different cocatalysts, such as: Au, Pt, Ag or Cu, for the sake of comparison. The samples were characterized using powder XRD, XPS, UV-visible, thermoluminescence, SEM, HRTEM and SAED techniques. Compared to other metal/TiO(2) photocatalysts, Au/TiO(2) with an optimum gold loading of 1 wt% was found to exhibit considerably higher activity for visible light induced production of H(2) from splitting water in the presence of methanol. Further, the sol-gel prepared TiO(2) (s.TiO(2)), having spherical grains of 10-15 nm size, displayed better photoactivity than a Degussa P25 catalyst. The electron microscopy investigations on s.TiO(2) revealed significant heterogeneity in grain morphology of individual TiO(2) particles, exposure of the lattice planes, metal dispersion, and the interfacial metal/TiO(2) contacts. The gold particles were found to be in a better dispersed state. O(2) TPD experiments revealed that the gold nanoparticles and Au/TiO(2) interfaces may serve as distinct binding sites for adsorbate molecules. At the same time, our thermoluminescence measurements provide an insight into Au-induced new defect states that may facilitate the semiconductor-to-metal charge transfer transition. In conclusion, the superior photocatalytic activity of Au/TiO(2) may relate to the grain morphology of TiO(2), dispersion of gold particles, and the peculiar architecture of metal/oxide heterojunctions; giving rise in turn to augmented adsorption of reactant molecules and their interaction with the photo-generated e(-)/h(+) pair. The role played by methanol as a sacrificial reagent in photocatalytic splitting of water is discussed.
ABSTRACT
To improve catalytic performance iron based catalyst, the effects of some metal promoters, especially potassium, copper and other transition metal oxides as well as different supports have been reported. A series of Fe/K/Cu catalysts promoted with magnesium and ceria by precipitation method, followed by impregnation method; keeping Cu and K content same. The catalysts were characterized by XRD, N2 physisorption, TPR and TEM techniques. From XRD, the presence of hematite (Fe2O3) phase was detected in all precipitated iron catalysts and CFe2.5 phase in all used catalysts. TPR results showed that addition of Mg facilitated the reduction of Fe2O3 and decrease in reduction temperature. The catalytic performance was investigated in a fixed-bed reactor at 250 degrees C, 2 MPa pressure and H2/CO molar ratio of 2. Concentration of Mg was found to affect the CO conversion and product distribution. It was found that precipitated iron catalyst Fe/Mg/Cu/K with Mg/Fe ratio of 0.1 showed highest conversion (60.6%) and C5(+) selectivity (92.4%) among all catalysts tested.
ABSTRACT
Nano-sized cobalt supported catalysts were prepared for Fischer-Tropsch synthesis in gas-to-liquid (GTL) process. The dependence of crystallite size and reducibility of Co3O4 on the supports were investigated with FTS activity. XRD peaks revealed nano crystallites (< 5.47 nm) of Co3O4 crystallites. TEM showed round shaped particles with size less than 5 nm. Support with higher acidity decreased crystallite size of Co3O4. XRD data of used catalysts showed Co3O4 crystallites smaller than 3.5 nm which do not reduce easily to Co(0) state. The crystallite size of Co3O4 plays a role in its reduction to Co(0). TPR results showed that the reduction temperature shifts to higher temperature due to metal-support interaction. The variation in the activity of the catalysts depends on the support which in turn affects the crystallite size, dispersion, reducibility and activity of Co species in Fischer-Tropsch Synthesis (FTS). In this study, Co/Al2O3 showed higher CO conversion than the other catalysts. However, the C5+ production was in order Co/SiO2 (78.1%) > Co/Al2O3 (70.0%) > Co/R_TiO2 (61%) > Co/A_TiO2 (57.5%).
