CO2 CONVERSION USING Mg2NiH4 SAMPLES WITH DIFFERENT MICROSTRUCTURE

M. L GRASSO; J. A. PUSZKIEL; C. PISTIDDA; F C GENNARI

Congreso; XXIX INTERNATIONAL MATERIALS RESEARCH CONGRESS; 2021

MRS

The current situation related to CO2 emissions promotes the development of capture and conversion technologies in the context of world decarbonization trend. These technologies allow to considerer CO2 us as feedstock in add-value compounds production (eg. synthetic fuels, polymers and alcohols). One of the considered process is the methanation, which allows CO2 conversion using a H2 source and species with catalytic role. Ni-based catalysts are commonly used in COx (CO2 or CO) conversion due to its high activity, selectivity to CH4 and low cost. However, it has as disadvantage the metal deactivation caused by superficial coke deposition and sintering effects. It was studied the catalytic properties of the Mg2NiH4 surface during CO2 methanation. In that reaction, hydrides participate as H2 source and catalyst providers. In this work, we studied the thermochemical reaction between CO2 and Mg2NiH4 using samples of hydrides with different microstructures. Two synthesis routes are considered to samples preparation: a two-step process (mechanical milling followed a high temperature and pressure treatment) and a reactive mechanochemical processing (in H2 atmosphere). The thermochemical reaction between samples was carried out under static conditions using a Sievert-type volumetric device with temperature and pressure control system. Then, each sample was heated until 400ºC under CO2 pressure (according its H2 storage capacity and H2:CO2 molar ratio of 4:1). Samples were analyzed thought structural, chemical and microstructural characterization techniques: XRD (X-ray diffraction), SEM (Scanning electron microscopy), FTIR (Fourier transformation infrared spectroscopy) and Raman spectroscopies. Additionally, thermodynamical calculations were made to compare with experimental data.The comparison of the behaviour of each Mg2NiH4 sample in CO2 evidences a high reactivity for nanostructured hydride given by the full CO2 consumption and hydride decomposition after 5 hours at 400ºC. Structural data shows the formation of solid products such as Ni-Mg2Ni-MgNi2/MgO with a potential catalytic role. In addition, experimental results and thermodynamical calculations suggest different reaction mechanism between each hydride and CO2 under considered conditions. We propose that the microstructure of Mg2NiH4 sample has an important role in the reactivity and reaction mechanism during CO2 conversion.