Novel bi-functional Ni–Mg–Al–CaO catalyst for catalytic gasification of biomass for hydrogen production with in situ CO2 adsorption

Abstract

Catalytic gasification of biomass in the presence of CaO is a promising route for CO₂ capture and thereby high yield hydrogen production. However, the instability of the CaO sorbent for CO₂ adsorption is a challenge for the process. A novel bi-functional Ni–Mg–Al–CaO catalyst has been prepared with different contents of CaO by integration of the catalytic and CO₂ adsorbing materials to maximise hydrogen production. The prepared catalysts were tested for hydrogen production via the pyrolysis-gasification of wood biomass using a two-stage fixed-bed reaction system. The carbonation/calcination results using thermogravimetric analysis (TGA), in an atmosphere of N₂ or CO₂, showed that the reactivity of CaO with CO₂ decreased even after several cycles of carbonation/calcination, while the Ni–Mg–Al–CaO catalyst showed a comparatively stable CO₂ adsorption even after 20 cycles. Adding CaO to the Ni–Mg–Al catalyst leads to an increase in hydrogen production and selectivity due to the enhancement of the water–gas shift reaction by in situ CO₂ adsorption. An optimal content of CaO was suggested to be 20 wt% (weight ratio of CaO/Ni–Mg–Al) which gave the highest hydrogen production (20.2 mmol g⁻¹ biomass) in the presence of the Ni–Mg–Al–CaO catalyst. Temperature-programmed oxidation (TPO) showed that carbon deposition was significantly decreased with the addition of CaO in the Ni–Mg–Al catalyst, and with the increase of CaO content, coke deposition on the reacted catalyst was further decreased.