Study of X-ray photoelectron spectroscopy on coke deposited on Ni/HZSM-5 in bio-oil hydrodeoxygenation

The coke deposited on the surfaces of Ni/HZSM-5 catalyst in bio-oil hydrodeoxygenation (HDO) was characterized by using a technique of X-ray photoelectron spectroscopy. The results show that the compounds with carbon related oxygen are the main constituent of the coke on the Ni/HZSM-5 catalysts. The amount of carbon compounds with two oxygen atoms is decreased with increasing reaction temperature due to their splitting by activated H-2 during HDO processing of bio-oil. Carbon compounds with one oxygen atom are changed during the HDO of bio-oil processing, where soluble carbon compounds were converted to insoluble ones, with increasing reaction temperature leading to increase in hard carbon compounds. Graphite appeared on the surface of the Ni/HZSM-5 catalysts in the HDO of bio-oil at the highest temperature in the experiments. The related mechanism is presented in the paper.