CeO₂ and TiO₂ support material effects on NH₃ decomposition pathway mechanism over Cu-Zn catalysts

The decomposition of NH3 over Cu-Zn catalysts, supported on ceria and titania, was investigated, producing carbon (di)oxide-free H-2. The rate of the H-2 formation at the exposed metallic Cu atoms (cumulative turnover frequency) for dispersed Cu-Zn depended strongly on the type of metal oxide support, indicating that the pathway active sites of Cu-Zn nano-catalysts were not identical in quantity. The investigation of the associative desorption process of atomic nitrogen moieties formed by the NH3 scission over Cu-Zn alloy revealed that N-2 interface evolution temperature was affected by the nature of substrates. The characterization of the nano materials before the catalyzed splitting reactions of NH3 was carried out by XRD, N-2 physisorption, N2O chemisorption, H-2 TPD, CO2 TPD, NH3 TPD and H-2 TPR. TEM and XPS were conducted on both fresh and used composites. Cu-Zn dispersion increased in the presence of TiO2. These spinel forms exhibited a strong Cu0.5Zn0.3Ti0.2O2-x (x = 0-1) structure interaction. Cu-Zn/CeO2 showed a 79% conversion of ammonia at 600 degrees C, whereas Cu-Zn/TiO2 demonstrated 63% at comparative operating conditions. A high catalytic activity, reflected in almost total consumption of ammonia at 700 degrees C with the hydrogen reactive production of 33.2 mmol g(-1) min(-1), was achieved over Cu-Zn/TiO2. No reactivity loss considering the NH3 depletion under applied reactor runs was detected, implying that materials had excellent time-on-stream stability. By scanning and transmission electron microscopy, bimetallic Cu-Zn was also observed, displaying a uniform TiO2 particle distribution on a structured sample surface. Impregnated zinc and copper species were uniformly distributed over Cu-Zn/TiO2. In the case of higher precursor content, a slight Cu domain agglomeration was noted. A heterogeneous mixed phase of Cu and Cu2O was present in all examined powders, as exposed by Cu L-edge spectra ratios.