A density functional theory study of Nix (x = 4–16) cluster impregnation effects in multi-metal (Ce, Ti) UiO-66 metal–organic frameworks

Abstract

Nickel (Ni) has been used as an active metal component catalyst for attaining high conversion in the tri-reforming of methane (TRM) reaction, which produces synthesis gas as a product. Impregnation of Ni within the multi-metal MOF (MM-MOF) materials results in enhanced catalytic activity for TRM. In this work, we have studied the properties of a Ni-cluster impregnated within a metal (Ce or Ti) doped UiO-66 MOF using density functional theory (DFT) calculations. Different amounts of cerium (Ce) or titanium (Ti) metals are doped (16.67% and 33.3%) in the UiO-66 structure, and different sizes of Ni_x clusters (x = 4–16) are impregnated in the pores of the MM-MOF structure. With increasing Ce-substitution, the MM-MOF shows better improvement in the Ni_x binding energy per Ni atom compared to Ti-substitution. Furthermore, projected density of state (PDOS) calculations reveal that while a charge localization occurs at the Ce site, no such charge localization is observed at the Ti site. Our results demonstrate that the strong binding of Ni clusters not only depends on the electron rearrangement but also depends on the structural stability of MOF materials. These atomic insights may be helpful in the synthesis of future stable and sustainable, catalytic hybrid MOF materials for energy and environmental applications.