Abstract:
A series of copper ion substituted MAl(2)O(4) (M = Mg, Mn, Fe and Zn) spinels is prepared by a single step solution combustion synthesis (SCS) and tested for methanol steam reforming (MSR). The copper ion substituted Cu(0.1)Fe(0.9)Al(2)O(4) appears to be the most active, showing approx. 98 percent methanol conversion at 300 degrees C with approx. 5 percent CO selectivity at GHSV = 30,000 h sup(-1) and H(2)O:CH(3)OH = 1.1. The analogous impregnated catalyst, CuO (10 at percent)/FeAl(2)O(4), is found to be much less active. These materials are characterized by XRD, H(2)-TPR, BET, HRTEM, XPS and XANES analyses. Spinel phase formation is highly facilitated upon Cu-ion substitution and Cu loading beyond 10 at percent leads to the formation of CuO as an additional phase. The ionic substitution of copper in FeAl(2)O(4) leads to the highly crystalline SCS catalyst containing Cu sup(2+) ion sites that are shown to be more active than the dispersed CuO nano-crystallites on the FeAl(2)O(4) impregnated catalyst, despite its lower surface area. The as prepared SCS catalyst contains also a portion of copper as Cu sup(1+) that increases when subjected to reforming atmosphere. The MSR activity of the SCS catalyst decreases with time-on-stream due to the sintering of catalyst crystallites as established from XPS and HRTEM analyses.
