Band-Gap Engineering: A New Tool for Tailoring the Activity of Semiconducting Oxide Catalysts for CO Oxidation

Thermocatalytic Degradation of Gaseous Formaldehyde Using Transition Metal-Based Catalysts

Formaldehyde (HCHO: FA) is one of the most abundant but hazardous gaseous pollutants. Transition metal oxide (TMO)-based thermocatalysts have gained much attention in its removal due to their excellent thermal stability and cost-effectiveness. Herein, a comprehensive review is offered to highlight the current progress in TMO-based thermocatalysts (e.g., manganese, cerium, cobalt, and their composites) in association with the strategies established for catalytic removal of FA. Efforts are hence made to describe the interactive role of key factors (e.g., exposed crystal facets, alkali metal/nitrogen modification, type of precursors, and alkali/acid treatment) governing the catalytic activity of TMO-based thermocatalysts against FA. Their performance has been evaluated further between two distinctive operation conditions (i.e., low versus high temperature) based on computational metrics such as reaction rate. Accordingly, the superiority of TMO-based composite catalysts over mono- and bi-metallic TMO catalysts is evident to reflect the abundant surface oxygen vacancies and enhanced FA adsorptivity of the former group. Finally, the present challenges and future prospects for TMO-based catalysts are discussed with respect to the catalytic oxidation of FA. This review is expected to offer valuable information to design and build high performance catalysts for the efficient degradation of volatile organic compounds.

Development of defective molybdenum oxides for photocatalysis, thermal catalysis, and photothermal catalysis

The localized surface plasmon resonance (LSPR) of noble metals has been investigated for decades for applications in various catalysis reactions and optical research studies, but its development has been hampered by inefficient light absorption and high costs. In comparison, the creation of less expensive semiconductors (metal oxides) with strong plasmonic absorption is an appealing option, particularly defective molybdenum oxide (H_xMoO_3-y) has received considerable attention and investigation as a promising plasmonic material for a variety of catalytic reactions (photocatalysis, thermocatalysis, photothermal catalysis, etc.).The LSPR effect of H_xMoO_3-y can be tuned throughout a broad spectrum range from visible to near-infrared (NIR) by altering the doping amount by electrochemical control, chemical reduction, or photochemical control. Notably, defects (oxygen vacancies) in H_xMoO_3-y arise in conjunction with the LSPR effect, resulting in the formation of unique and useful active sites in a range of catalytic processes. In this review, we explore the formation mechanism of H_xMoO_3-y with plasmonic features and discuss its applications in photocatalysis, thermocatalysis, and photothermal catalysis.

Metal-Free Boron/Phosphorus Co-Doped Nanoporous Carbon for Highly Efficient Benzyl Alcohol Oxidation

An in-depth understanding of the electronic structures of catalytically active centers and their surrounding vicinity is key to clarifying the structure-activity relationship, and thus enabling the design and development of novel metal-free carbon-based materials with desired catalytic performance. In this study, boron atoms are introduced into phosphorus-doped nanoporous carbon via an efficient strategy, so that the resulting material delivers better catalytic performance. The doped B atoms alter the electronic structures of active sites and cause the adjacent C atoms to act as additional active sites that catalyze the reaction. The B/P co-doped nanoporous carbon shows remarkable catalytic performance for benzyl alcohol oxidation, achieving high yield (over 91% within 2 h) and selectivity (95%), as well as low activation energy (32.2 kJ mol^-1 ). Moreover, both the conversion and selectivity remain above 90% after five reaction cycles. Density functional theory calculations indicate that the introduction of B to P-doped nanoporous carbon significantly increases the electron density at the Fermi level and that the oxidation of benzyl alcohol occurs via a different reaction pathway with a very low energy barrier. These findings provide important insights into the relationship between catalytic performance and electronic structure for the design of dual-doped metal-free carbon catalysts.