Search

A ZnO-nanolayer-coated carbon nanotube (CNT) composite (ZnO-CNT) was employed as a support to immobilise Ni catalysts. Well-mixed oxides, formed as a result of enhanced interfaces between the two oxides on CNTs, resulted in the formation of Ni-Zn alloys in reduced catalysts. The Ni/ZnO-CNT catalyst exhibited much higher yields of vicinal diols, for example, ethylene glycol and 1,2-propylene glycol, from the conversion of cellulose than the reference Ni/CNT catalyst. A plausible reaction network on the Ni/ZnO-CNT catalyst has been proposed. Moreover, the effects of Ni loading and catalyst reduction temperature on the catalytic performance were probed, and the relationship between the catalyst structure and the yields of vicinal diols was correlated. The Ni-rich alloy, relative to the Zn-rich alloy, was suggested as the dominating active phase for the selective conversion of cellulose into vicinal diols. This might shed new light on the design and optimisation of Ni-based catalysts for the catalytic conversion of cellulose with the Ni-Zn interaction. [ABSTRACT FROM AUTHOR]

Ni-carbon nanofibers (Ni-CNFs) catalysts were synthesizedin situby the decomposition of carbon-containing gases (i.e., CH4, CO, and C2H4) over Ni/Al2O3catalyst and directly used to catalyze ammonia decomposition.The results showed that Ni nanoparticles were found to locate at thetips of CNFs when using CH4and CO as carbon sources, whilethey located at the roots of CNFs when using C2H4as a carbon source. For ammonia decomposition, Ni catalysts at thetips of CNFs showed higher activity, which could be due to the moreaccessible surfaces to the reactants. Interestingly, the Ni catalystat the tips of CNFs with CH4as a carbon source exhibitedhigher activity than that with CO as a carbon source, even thoughthe former catalyst had a larger average particle size. The possiblemechanism was given by combining characterization results with ourprevious simulation results. Finally, when using CH4asa carbon source, the effect of the Ni-CNFs catalysts with differentgrowth times on the activity was further studied. [ABSTRACT FROM AUTHOR]

Abstract: First-principles calculations have been performed to examine the effect of doped Ag on the kinetics of Ni-catalyzed methane dissociation and coke formation. The close-packed Ag/Ni(111) and stepped Ag/Ni(211) surfaces as well as the defect facets with step sites blocked by Ag or C atoms are constructed to investigate the role of the coordinatively unsaturated sites in the catalytic performance of Ni nanoparticles. The most stable CH x (x =0–4) adsorption configurations and transition states for methane dissociation have been identified on both Ni and Ag/Ni surfaces. The calculated results indicate that the activation energy for methane dissociation is increased with the Ag coverage on Ni(111), and the C atoms deposited on the catalyst surface can be readily separated into small islands by Ag. On Ni(211) Ag atoms are predicted to bind preferentially to the middle-step sites which act as the nucleation center for the growth of filamentous carbon and therefore have the potential to prevent catalyst particles from being destroyed. Meanwhile, as the energy barrier for methane dissociation on the Ag-blocked Ni(211) surface is even higher than that on pure Ni(111), the active center is transferred from the stepped surface to the close-packed surface. These findings provide a rational interpretation of the experimental observations that Ag/Ni catalyst exhibits lower catalytic activity towards steam methane reforming but high resistance to coke deposition. [Copyright &y& Elsevier]