Selective enhancement of bio-oil from pyrolysis of corn stalk: A tandem dual-catalyst system of reduced red mud and Fe/Ca catalyst

To enhance the ketone and phenol contents in corn stover (CS) pyrolysis bio-oil, a tandem dual-catalyst system integrating reduced red mud (RRM) and a reduced Fe/Ca catalyst was employed. A systematic study was conducted, focusing on the effects of the Fe/Ca mass ratio, reduction temperature, pyrolysis temperature, and catalyst recycling on the content and selectivity of the target products. The reaction mechanisms underlying the enrichment of ketones and phenols were also elucidated. Results indicated that at an Fe/Ca mass ratio of 1:2 and a reduction temperature of 650 °C (FC2-R650), Fe/Ca displayed an increased number of surface oxygen vacancies, a greater abundance of acid-base sites, and enhanced textural properties manifested by an enlarged specific surface area and expanded pore volume. Its crystal structure was primarily composed of Ca 2 Fe 2 O 5 and CaO. The tandem catalysis enhances the efficiency of RRM in promoting reactions including cyclization, cross-ketonization, and alkylation- for pyrolysis vapor molecules. At the pyrolysis temperature of 500°C, the contents of phenols and ketones increased from 22.72 % and 30.51 % under RRM single-stage catalysis to 42.87 % and 37.31 % with tandem catalysis, while components such as carboxylic acids and light aldehydes were undetected. Recycling experiments confirmed the good cycling performance of the tandem catalytic system, with the content of ketones and phenols maintained at 73.67 % after three cycles. The tandem dual-catalyst system based on RRM and FC2-R650 offers an innovative catalytic strategy for the resource utilization of agricultural and industrial wastes, contributing to the production of sustainable fuels and high-value chemicals. • Reduced red mud (RRM) and complex Fe/Ca (FC2-R650) showed synergistic effects as tandem dual-catalyst. • RRM and FC2-R650 presented a positive effect on the contents of ketones and phenols. • The acids and light aldehydes were completely converted. • The catalytic mechanism of RRM and FC2-R650 was investigated.