Highly efficient Pd–ZnO catalyst doubly promoted by CNTs and Sc2O3 for methanol steam reforming Original Research Article

A type of Pd–ZnO catalyst doubly promoted by CNTs and Sc2O3 for methanol steam reforming (MSR) was developed, and displayed excellent activity and operation stability for the selective formation of H2 and CO2. Over a Pd0.15Zn1Sc0.067–10%CNTs catalyst under the reaction conditions of 0.5 MPa and 548 K, the STY(H2) can maintain stable at the level of 1.56 mol h−1 g−1 at 75 h after the reaction started, which was 1.7 times that of the corresponding (CNTs and Sc)-free counterpart Pd0.15Zn1. Characterization of the catalyst revealed that the highly conductive CNTs could promote hydrogen spillover from the PdZn/ZnO-sites to the CNTs adsorption-sites, and then combine to form H2(a), followed by desorbing to H2(g), which would help increase the rate of a series of surface dehydrogenation reactions in the MSR process. The pronounced modification action of Sc3+ may be due to the high solubility of Sc2O3 in ZnO lattice. Solution of a small amount of Sc2O3 in ZnO lattice resulted in the formation of Schottky defects in the form of cationic vacancies at the surface of ZnO, where the (PdZn)0–Pd2+ clusters can be better stabilized through the Pd2+ accommodated at the surface vacant cation-sites. This would be conducive to inhibiting the sintering of the catalytically active (PdZn)0 nanoparticles, and thus, markedly prolonging the life of the catalyst.