Highly Dispersed Ni0/NixMg1–xO Catalysts Derived from Solid Solutions: How Metal and Support Control the CO2 Hydrogenation

Marie-Mathilde Millet,Robert Schlögl,Frank Girgsdies,Andrey V Tarasov,Gerardo Algara-Siller,Elias Frei

doi:10.1021/acscatal.9b02332

Abstract

Among the Ni-based catalysts studied for CO2 activation reactions, NixMg1–xO solid solutions present advantageous characteristics, mainly linked with the homogeneous distribution of the Ni species inside the MgO structure, leading to highly dispersed Ni0 supported catalysts. In this work, we report on the preparation and characterization of NixMg1–xO precatalysts calcined at different temperatures. The resulting Ni0/NixMg1–xO catalysts were tested for the methanation of CO2. Following the structural, morphological, and chemical changes during both the calcination and the reduction, we were able to observe clear correlations between the reactivity of the catalysts and their physical properties, leading to a better understanding of the reaction mechanism and the respective contributions of the metal and the support. While no change was observed in the formation of CH4 over the range of temperature tested, the CO formation as byproduct clearly changed with the increasing temperatures. Our results are consistent with the hypothesis that two different CO formation mechanisms are occurring, but depending on the temperature, one dominates over the other. This study illustrates the importance of the complex interplay of metal particles and oxidic support (at the interface), both actively participating in the CO2 hydrogenation mechanism.

Highlights

CO2 is at the central stage of global warming as changes in climate can be partially attributed to anthropogenic greenhouse gas emissions
The Ni particles sizes are predetermined by the reducibility of the samples, which is in turn a function of the calcination temperature
The change in apparent activation energy would in this case reflect two competing reactions, involving different active sites, relevant in different temperature regimes

Summary

Introduction

CO2 is at the central stage of global warming as changes in climate can be partially attributed to anthropogenic greenhouse gas emissions. The use of CO2 as a chemical feedstock is limited to only a few industrial processes like the synthesis of urea, polycarbonates, salicylic acid, and methanol, representing only a small fraction of the potential CO2 available for conversion.[1] An effective way to reduce CO2 emissions is to use it as a component for the fuel pool, which worldwide consumption is 2 orders of magnitude higher than that of chemicals.[2] The products of CO2 hydrogenation such as hydrocarbons (e.g., CH4) present the advantage that they can be stored and transported .[3] For the methanation of carbon oxides, Ni has always been the catalytic material of choice, and this, since the very early studies of Paul Sabatier,[4] because of its high activity and selectivity toward methane, and its relatively low price compared to the noble metals active in COx hydrogenation (Ru, Ir, Rh, and Pd).[5]

Methods

Results

Conclusion