| Popis: |
Selective production of hydrogen by oxidative steam reforming of methanol (OSRM) was studied over Cu/SiO2 catalyst using fixed bed flow reactor. Textural and structural properties of the catalyst were analyzed by various instrumental methods. TPR analysis illustrates that the reduction temperature peak was observed between 510 K and 532 K at various copper loadings and calcination temperatures and the peaks shifted to higher temperature with increasing copper loading and calcination temperature. The XRD and XPS analysis demonstrates that the copper existed in different oxidation states at different conditions: Cu2O, Cu0, CuO and Cu(OH)2 in uncalcined sample; CuO in calcined sample: Cu2O and metallic Cu after reduction at 600 K and Cu0 and CuO after catalytic test. TEM analysis reveals that at various copper loadings, the copper particle size is in the range between 3.0 nm and 3.8 nm. The Cu particle size after catalytic test increased from 3.6 to 4.8 nm, which is due to the formation of oxides of copper as evidenced from XRD and XPS analysis. The catalytic performance at various Cu loadings shows that with increasing Cu loading from 4.7 to 17.3 wt%, the activity increases and thereafter it decreases. Effect of calcination shows that the sample calcined at 673 K exhibited high activity. The O2/CH3OH and H2O/CH3OH molar ratios play important role in reaction rate and product distribution. The optimum molar ratios of O2/CH3OH and H2O/CH3OH are 0.25 and 0.1, respectively. When the reaction temperature varied from 473 to 548 K, the methanol conversion and H2 production rate are in the range of 21.9–97.5% and 1.2–300.9 mmol kg−1 s−1, respectively. The CO selectivity is negligible at these temperatures. Under the optimum conditions (17.3 wt%, Cu/SiO2; calcination temperature 673 K; 0.25 O2/CH3OH molar ratio, 0.5 H2O/CH3OH molar ratio and reaction temperature 548 K), the maximum hydrogen yield obtained was 2.45 mol of hydrogen per mole of methanol. The time on stream stability test showed that the Cu/SiO2 catalyst is quite stable for 48 h. Keywords: Cu/SiO2, Nanoparticle, Urea, Hydrogen production, Oxidative steam reforming, Methanol |
