The promotional effects of plasma treating on Ni/Y2Ti2O7 for steam reforming of methane (SRM): Elucidating the NiO-support interaction and the states of the surface oxygen anions

To explore the interaction between NiO and Y2Ti2O7 support, and fabricate improved catalysts for SRM, several Ni/Y2Ti2O7 catalysts have been prepared by an impregnation method with the assistance of dielectric barrier discharge (DBD) plasma treating in different atmospheres. It is found that both the reaction performance and anti-coking ability are improved for the catalysts in comparison with the untreated sample, following the sequence of Ni/Y2Ti2O7-H2P > Ni/Y2Ti2O7-ArP > Ni/Y2Ti2O7-AirP > Ni/Y2Ti2O7. H-2-TPR and XPS results have demonstrated that plasma treatment effectively strengthens the interaction between NiO and Y2Ti2O7 support, and Ni2+ cations preferentially interact solely with the Y3+ cations in the A site of Y2Ti2O7. As a consequence, the agglomeration of the metallic Ni species during the reduction process can be impeded, thus obtaining catalysts possessing higher Ni dispersion. As evidenced by Raman, EPR and XPS results, superoxide O-2(-) anions induced by the intrinsic 8a oxygen vacancies of Y2Ti2O7 pyrochlore phase is the only kind of active surface oxygen sites, which might play a critical role for coking removing, and whose formation can be significantly facilitated by plasma treating. In conclusion, the improved active Ni surface area and the surface active superoxide O-2 amount by DBD plasma treating are the major factors responsible for the enhanced reaction performance and coking resistance of the catalysts. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.