Adsorption Characteristics of Gas Molecules (H2O, CO2, CO, CH4, and H2) on CaO-Based Catalysts during Biomass Thermal Conversion with in Situ CO2 Capture

Baofeng Zhao,Shuangxia Yang,Haibin Guan,Laizhi Sun,Ge Song,Di Zhu,Jingwei Wang,Huajian Yang,Lei Chen,Xinping Xie

doi:10.3390/catal9090757

Abstract

Biomass thermochemical conversion with in situ CO2 capture is a promising technology in the production of high-quality gas. The adsorption competition mechanism of gas molecules (H2O, CO2, CO, CH4, and H2) on CaO-based catalyst surfaces was studied using density functional theory (DFT) and experimental methods. The adsorption characteristics of CO2 on CaO and 10 wt % Ni/CaO (100) surfaces were investigated in a temperature range of 550–700 °C. The adsorption energies were increased and then weakened, reaching their maximum at 650 °C. The simulation results were verified by CO2 temperature-programmed desorption (CO2-TPD) experiments. By the density of states and Mulliken population analysis, CaO doped with Ni caused a change in the electronic structure of the Osurf atom and decreased the C–O bond stability. The molecular competition mechanism on the CaO-based catalyst surface was identified by DFT simulation. As a result, the adsorption energies decreased in the following order: H2O > CO2 > CO > CH4 > H2. The increase of CO2 adsorption energy on the 10 wt % Ni/CaO surface, compared with the CaO surface, was the largest among those of the studied molecules, and its value increased from 1.45 eV to 1.81 eV. Therefore, the 10 wt % Ni/CaO catalyst is conducive to in situ CO2 capture in biomass pyrolysis.

Highlights

Biomass thermochemical conversion with in situ CO2 capture technology is one of the hotspots in biomass energy utilization research, which can produce high-quality fuel gas with a wide range of applications [1,2,3,4,5]
In order to enhance CO2 adsorption capacity, CaO-based catalysts have been studied in biomass thermochemical conversion with in situ CO2 capture [1,2,3,11,12,13,14,15,16]
Charisiou et al [12] investigated the catalytic performance of H2 production through the glycerol steam reforming reaction (GSR) of nickel catalysts supported on CaO–MgO–Al2 O3

Summary

Introduction

Biomass thermochemical conversion with in situ CO2 capture technology is one of the hotspots in biomass energy utilization research, which can produce high-quality fuel gas with a wide range of applications (alcohol/ether fuel synthesis, hydrogen fuel cells, etc.) [1,2,3,4,5]. The adsorption characteristics of CaO-based catalysts are impacted by multiple reactions and a large number of intermediates (CO2 , H2 O, CO, H2 , CH4 , toluene, etc.) in the process of biomass thermal conversion with in situ CO2 capture, which cannot be explained by experiments. The adsorption characteristics of CO2 on the surface of CaO and 10 wt % Ni/CaO catalysts at different temperatures in a biomass catalytic pyrolysis system were studied by DFT simulation and experimental methods. The feasibility of DFT method was verified Based on this premise, the adsorption behaviors of other molecules (CO, H2 O, H2 , and CH4 ) on CaO and 10 wt % Ni/CaO (100) surfaces were further simulated to provide theoretical support for an in-depth analysis of complex catalytic reactions in biomass pyrolysis with in situ CO2 capture and production of high-quality gas

Results and Discussion

Results at at Different

Computational

Experimental Details

Conclusions