Development of LaFeO3 modified with potassium as catalyst for coal char CO2 gasification

Coal catalytic gasification is an effective way to realize clean coal utilization. The core of this technology is the preparation of highly efficient and stable catalysts. At present, perovskite-type oxides have attracted increasing attention as a promising catalyst because of its good thermal stability and redox activity. In this study, perovskite-type oxides were proposed to act as catalyst for coal char CO2 gasification, and K was further used for LaFeO3 catalyst modification to improve its catalytic activity. The catalytic performances of La1-xKxFeO3 (x= 0-0.9) were tested by thermogravimetric analysis and fixed-bed tube reactor. The crystal structure was determined by X-ray diffraction (XRD), the percentage content and valence state of surface elements were examined by X-ray photoelectron spectroscopy (XPS), the surface morphology of perovskite samples was observed by scanning electron microscopy (SEM). Besides, the specific surface area and average particle diameter were analyzed by N2 absorption/desorption technology (BET) and laser particle size analyzer, respectively. Results suggested that the perovskite-type catalyst can effectively lowered the initial reaction temperature and exhibited improved catalytic activity after a part of La3+ at A-site was replaced by K+. The time required to achieve 50% carbon conversion in the initial reaction was reduced by 87.3% when the molar ratio of K+ increased from 0 to 0.7. The La0.3K0.7FeO3 perovskite also exhibited relatively stable catalytic activity during cyclic process, and its optimal temperature in coal char CO2 gasification was approximately 850 degrees C. The XRD patterns indicated that the perovskite structure of catalyst can remain unchanged when K+ doping ratio was lower than 0.8. Therefore, 0.7 is a suitable doping ratio. The perovskite La0.3K0.7FeO3 still exhibited perovskite crystal structure after 10 cycles of experiment. The XPS results indicated that additional oxygen vacancies and Fe4+ formed after K+ doping, which contributed to gas adsorption and electron transfer and improved oxidation performance. SEM and BET showed that the pore structure of catalyst was destroyed during cyclic gasification, resulted in the enlargement of particle size detected by laser particle size analyzer. Leading to the decrease in effective contact area and catalytic performance. Thus, K+-modified perovskite La1-xKxFeO3 is a kind of equipment-friendly, efficient and recyclable catalyst and can be used as a promising catalyst for coal char CO2 gasification.