Atomic layer deposition (ALD) has emerged as an interesting tool for the atomically precise design and synthesis of catalytic materials. Herein, we discuss examples in which the atomic precision has been used to elucidate reaction mechanisms and catalyst structure–property relationships by creating materials with a controlled distribution of size, composition, and active site. We highlight ways ALD has been utilized to design catalysts with improved activity, selectivity, and stability under a variety of conditions (e.g., high temperature, gas and liquid phase, and corrosive environments). In addition, due to the flexibility and control of structure and composition, ALD can create myriad catalytic structures (e.g., high surface area oxides, metal nanoparticles, bimetallic nanoparticles, bifunctional catalysts, controlled microenvironments, etc.) that consequently possess applicability for a wide range of chemical reactions (e.g., CO₂ conversion, electrocatalysis, photocatalytic and thermal water splitting, methane conversion, ethane and propane dehydrogenation, and biomass conversion). Finally, the outlook for ALD-derived catalytic materials is discussed, with emphasis on the pending challenges as well as areas of significant potential for building scientific insight and achieving practical impacts.

Discharging dye contaminants into water is a major concern around the world. Among a variety of methods to treat dye-contaminated water, photocatalytic degradation has gained attention as a tool for treating the colored water. Herein, we review the recent advancements in photocatalysis for dye degradation in industrial effluents by categorizing photocatalyst materials into three generations. First generation photocatalysts are composed of single-component materials (e.g., TiO₂, ZnO, and CdS), while second generation photocatalysts are composed of multiple components in a suspension (e.g., WO₃/NiWO₄, BiOI/ZnTiO₃, and C₃N4/Ag₃VO₄). Photocatalysts immobilized on solid substrates are regarded as third generation materials (e.g., FTO/WO₃-ZnO, Steel/TiO₂-WO₃, and Glass/P-TiO₂). Photocatalytic degradation mechanisms, factors affecting the dye degradation, and the lesser-debated uncertainties related to the photocatalysis are also discussed to offer better insights into environmental applications. Furthermore, quantum yields of different photocatalysts are calculated, and a performance evaluation method is proposed to compare photocatalyst systems for dye degradation. Finally, we discuss the present limitations of photocatalytic dye degradation for field applications and the future of the technology. Open image in new window

Hydrodeoxygenation (HDO) using heterogeneous catalysts has received considerable attention as a way of converting biomass-derived oxygenates into renewable fuels and chemicals. HDO involves a combination of different reactions such as hydrogenation, hydrogenolysis, decarbonylation, and dehydration. These reactions occur at different catalytic sites, typically with heterogeneous catalysts (e.g., metal, acid, and bifunctional sites), making HDO reactions complex. Therefore, the selection of active site type is critical when designing effective heterogeneous catalysts for HDO processes. Catalyst stability is a major issue in designing HDO catalysts. Traditional catalysts are not stable under HDO conditions (i.e., high partial pressure of water). Metal particles are leached and/or sintered. A solid acid support suffers from phase transformation and losses in surface area. The condensation or polymerization of the CC or CO bond within biomass and its derived oxygenates is easy to undertake under high temperatures in the HDO process, causing carbon deposition on the catalyst. Poor catalyst stability is a major challenge that needs to be overcome for innovation in HDO technologies. Therefore, herein, we focus on providing an insight into how to design effective catalysts for use in HDO reactions. First, the roles of different catalytic sites in HDO and strategies to stabilize these active sites are discussed. Current achievements in the HDO of different biomass feedstocks (e.g., model compounds and bio-oils) over various heterogeneous catalysts are highlighted. Recent developments in electrochemical HDO processes, which do not require gaseous hydrogen, are discussed. Finally, points to be considered for further research into HDO over heterogeneous catalysts and pending challenges are discussed.

The tremendous amount of food waste from diverse sources is an environmental burden if disposed of inappropriately. Thus, implementation of a biorefinery platform for food waste is an ideal option to pursue (e.g., production of value-added products while reducing the volume of waste). The adoption of such a process is expected to reduce the production cost of biodegradable plastics (e.g., compared to conventional routes of production using overpriced pure substrates (e.g., glucose)). This review focuses on current technologies for the production of polyhydroxyalkanoates (PHA) from food waste. Technical details were also described to offer clear insights into diverse pretreatments for preparation of raw materials for the actual production of bioplastic (from food wastes). In this respect, particular attention was paid to fermentation technologies based on pure and mixed cultures. A clear description on the chemical modification of starch, cellulose, chitin, and caprolactone is also provided with a number of case studies (covering PHA-based products) along with a discussion on the prospects of food waste valorization approaches and their economic/technical viability.