Catalyst Deactivation, Poisoning and Regeneration

Simultaneously Producing H2 and H2O2 by Photocatalytic Water Splitting: Recent Progress and Future

The solar-driven overall water splitting (2H2O→2H2 + O2) is considered as one of the most promising strategies for reducing carbon emissions and meeting energy demands. However, due to the sluggish performance and high H2 cost, there is still a big gap for the current photocatalytic systems to meet the requirements for practical sustainable H2 production. Economic feasibility can be attained through simultaneously generating products of greater value than O2, such as hydrogen peroxide (H2O2, 2H2O→H2 + H2O2). Compared with overall water splitting, this approach is more kinetically feasible and generates more high-value products of H2 and H2O2. In several years, there has been an increasing surge in exploring the possibility and substantial progress has been achieved. In this review, a concise overview of the importance and underlying principles of PIWS is first provided. Next, the reported typical photocatalysts for PIWS are discussed, including commonly used semiconductors and cocatalysts, essential design features of these photocatalysts, and connections between their structures and activities, as well as the selected approaches for enhancing their stability. Then, the techniques used to quantify H2O2 and the operando characterization techniques that can be employed to gain a thorough understanding of the reaction mechanisms are summarized. Finally, the current existing challenges and the direction needing improvement are presented. This review aims to provide a thorough summary of the most recent research developments in PIWS and sets the stage for future advancements and discoveries in this emerging area.

Comparison of the Accelerated and Spontaneous Deactivation of the HDS Catalyst

Owing to the increased use of secondary materials for diesel production, refineries must confront bad quality parameters. Therefore, catalysts with certain capabilities (to remove heteroatoms and improve quality parameters at low hydrogen consumption) and their lifetimes are required. An important parameter that influences the quality of the products and the economy of the unit is the activity of the catalyst. Prior to industrial use, the catalyst is typically tested in a pilot unit. This is necessary to obtain a considerable amount of data on the lifetime of the catalyst in the shortest feasible time. Here, deactivation steps were used to test the catalyst. Two experiments were performed to evaluate the effect of two types of accelerated deactivations on the catalyst activity and product properties. The first type of deactivation proceeded for 6 h and comprised a tripling of the amount of incoming feedstock, and the second type proceeded for 18 h without an increase in the amount of feedstock. For both cases, the pressure and hydrogen flow were minimised. Both types of accelerated deactivations had similar effects on the quality of the final products and catalyst. The only difference was in the duration of catalyst recovery after deactivation. The results were compared with those of a test in which the spontaneous deactivation of the catalyst was studied.

Hydrometallurgical Recovery of Cobalt(II) from Spent Industrial Catalysts

The work presents studies on the application of hydrometallurgical recovery of cobalt(II) from solutions after leaching spent industrial catalysts used in process of hydrodesulfurization. A four-stage process was proposed, which consists of: leaching, precipitation of metal hydroxides accompanying Co(II), extraction of Co(II) with bis(2,4,4-trimethylpentyl)phosphinic acid and Co(II) stripping from the organic phase. The results indicate that by using the proposed method it is possible to leach Co(II) and Mo(VI) from spent catalyst, and remove main impurities such as Al(III), Fe(III) in hydroxide precipitation step and separate Co(II) from Mo(VI) by extraction and stripping.