An Experimental Investigation of the Catalytic Activity of Natural Calcium-Rich Minerals and a Novel Dual-Supported CaO–Ca12Al14O33/Al2O3 Catalyst for Biotar Steam Reforming

Tar removal plays a key role in the process efficiency and viability of biomass gasification for syngas production applications. Among currently available tar treatment technologies, catalytic cracking was found to be the most attractive due to minimal energy losses by avoiding cooling of the raw product gas. Naturally available calcium-based catalysts, particularly stone dust and dolomite, have been proven to be effective for biotar cracking; however, they have poor resistance to attrition and undergo deactivation after a few carbonation/calcination cycles. As such, these characteristics play a critical role in determining the viability of their application at a large-scale. Hence to overcome the shortcomings previously stated, a novel dual supported calcium-based catalyst which includes a stable support with great mechanical strength (alumina, Al₂O₃, and mayenite, Ca₁₂Al₁₄O₃₃) dosed with CaO nanoparticles was synthesized by wet impregnation of calcium on alumina particles with and without the assistance of ultrasonication, referred to as CA and CAU respectively. The synthesized catalysts, as well as the naturally occurring calcium rich minerals stone dust and dolomite, were physically and chemically characterized using a variety of analytical techniques. The synthesized catalysts showed superior mechanical strength up to 5 times greater than the natural minerals. Each of the natural and synthesized catalysts was then investigated in a fixed bed reactor for steam reforming of biotars. In these experiments, toluene was used as a model tar compound to assess the catalytic activity of each and determine the best option in terms of catalytic activity, cost, and mechanical strength. The synthesized CA catalyst without ultrasonic treatment exhibited better tar cracking performance in comparison to stone dust and dolomite in the temperature range of 600 to 800 °C. The synthesized CA catalyst also had the greatest performance in terms of superior surface area and mechanical strength due to the core support of Al₂O₃. This makes it a potential bed material for further study of tar cracking in large-scale fluidized applications.