Partial oxidation of methanol for hydrogen production over carbon nanotubes supported Cu-Zn catalysts

Carbon nanotubes (CNTs) were used as support to Cu-Zn catalysts and tested their feasibility for hydrogen production from partial oxidation of methanol. The CNTs were synthesized by CVD method using acetylene as carbon source over anodic aluminum oxide template. The structural characteristics of CNTs were analysed by SEM, TEM, XRD, Raman spectroscopy and TGA. Using these CNTs as support, Cu-Zn catalysts with varying metal loading were prepared by co-precipitation method. The reducibility of the catalysts was tested with H2-TPR. N2 adsorption and CO chemisorption were used to monitor the surface area and total CO uptake of catalysts, respectively. The metal particle size of Cu-Zn/CNTs catalysts were measured from XRD and TEM. The nature of copper species and acidity were analysed by DRIFT study of CO adsorption and pyridine adsorption method, respectively. The deposition of Cu on CNTs surface resulted in creation of strong Lewis acid sites. The methanol conversion rate and H2 selectivity are increased from 0.066 to 0.11 mol/h/g cat and 57 to 70.6%, respectively, when increasing Cu loading from 5 to 12 wt% at 260 °C and further increase shows a fall in activity. The enhanced activity of 12 wt% Cu-9 wt% Zn/CNTs is due to the improved metal dispersion, narrow particle size distribution and almost complete reduction of Cu particles. The XRD analysis of spent catalyst indicates that during the POM reaction, the active Cu0 species is slowly converted into CuO, which is responsible for fall in activity.