Research development of processes for refining bio‐oils is becoming increasingly popular. One issue that these processes possess is their high requirement for H₂ gas. In response, researchers must develop catalysts that perform deoxygenation while minimizing H₂ consumption—selective deoxygenation. Unlike traditional deoxygenation processes, selective deoxygenation reactions and catalysts represent an information gap that, prior to this publication, has yet to be reviewed. This review addresses the gap by providing both a summary of recent research developments and insight into future developments of new catalytic materials. Bifunctional catalysts containing a combination of oxophilicity and an active metal phase appear to be the most beneficial for selective deoxygenation processes in a H₂‐modest environment. It is important that catalysts have a supply of disassociated hydrogen, because without such, activity and stability will suffer. The authors recommend to maximize the use of internally available hydrogen in bio‐fuel, which may be the only viable approach for deoxygenation if external H₂ gas is limited. This would be possible through the development of catalysts that promote both the water–gas‐shift and deoxygenation reactions.

Waste cooking oil (WCO) hydrotreating to produce green diesel is good for both the environmental protection and energy recovery problems. The roles of catalyst support and reaction temperature on reactions during WCO hydrotreating process were evaluated over an unsupported and a commercial sulfided cobalt and molybdenum (CoMoS) catalyst supported by a mixture of Al₂O₃, TiO₂, and SiO₂. The presence of catalyst support helped to improve the dispersion and enlarge the surface area of CoMoS, and was found to be a key factor in reducing reaction temperature, in enhancing the hydrodeoxygenation (HDO) and hydrogenation capabilities, and in decreasing polymerization capability. The increase of reaction temperature strongly improved the deoxygenation, hydrogenation, and cracking reaction activities. Compared to the unsupported CoMoS, the supported one exhibited good deoxygenation and hydrogenation capabilities at 340 °C in WCO hydrotreating to produce diesel fraction; however, high temperature operation needs to be carefully controlled because it may cause overcracking and dehydrogenation.

Light cycle oil (LCO) is one of the major products in Fluid catalytic cracking (FCC) processes, and has drawbacks such as high aromatics, sulfur, and nitrogen contents, and low cetane number (CN). Hydro-upgrading is one of the most typical processes for LCO upgrading, and alumina-zeolite (AZ) is an effective hydrotreating catalyst support. This paper examined the effects of different bimetallic catalysts (CoMo/AZ, NiMo/AZ, and NiW/AZ) supported by AZ on hydro-upgrading of both model compounds and real LCO. CoMo/AZ preferred the direct desulfurization (DDS) route while the NiMo/AZ and NiW/AZ catalysts favored the desulfurization route through hydrogenation (HYD). The presence of nitrogen compounds in the feed introduced a competitive adsorption mechanism and reduced the number of available acid sites. Aromatics were partially hydrogenated into methyltetralines at first, and then further hydrogenated, cracked, and isomerized into methyldecalins, monocyclic, and methyltetralines isomers. CoMo/AZ is the best hydrodesulfurization (HDS) catalyst for the model compounds at low H₂ pressure (550 psi) and for LCO at lower temperature (573 K), while NiMo/AZ performs the best for LCO at higher temperature (648 K). NiMo/AZ is the best hydrodenitrogenation (HDN) catalyst for LCO. The hydrodearomatization (HDA) performances of NiMo/AZ and NiW/AZ improved significantly and overwhelmingly higher than that of the CoMo/AZ when the H₂ pressure was increased to 1100 psi.

The exponential and continuous growth in the production and consumption of plastics, particularly polyethylene terephthalate (PET), due to their versatile applicability, has led to the accumulation of persistent plastic waste in the environment. This has created an urgent need to develop more sustainable and efficient recycling technologies. Although several recycling methods, such as mechanical and chemical recycling, have been implemented on an industrial scale, existing technologies still do not fully recover PET to its original quality or rely heavily on hazardous chemicals at elevated operating conditions. In this study, we explored a greener approach for PET depolymerization through hydrolysis under milder conditions, enhanced by mechanochemical degradation via ultrasonication, and integrated with UV-assisted treatment using five heterogeneous catalysts (ZnO, ZnFe₂O₄, Fe₂O₃, Y₂O₃, and SrO). The results of this study proved the significance of the mechanochemical effect of ultrasonication, which enhanced PET degradation by promoting chain scission, achieving up to 21.5% PET conversion and 19.0% terephthalic acid (TPA) yield in 1M NaOH hydrolysis. Among the catalysts tested under 0.1M NaOH hydrolysis, SrO exhibited the highest catalytic performance due to the formation of Sr(OH)2, which provides additional hydroxide ions for ester bond cleavage. However, excessive SrO loading led to SrSO₄ precipitation during acidification, requiring additional purification of the TPA product.