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Photoelectrochemistry (PEC) transfers photoexcited electrons from a photocatalyst to a cathode through a wire, to avoid, to a considerable extent, the recombination of charge carriers in solitary photocatalysis. The moderate bias also consumes less energy than electrocatalysis, rendering PEC a green and promising transformation approach. PEC biomass conversion can be performed at a lower bias than PEC water splitting, and biomass holds great potential for valorization as the world's largest renewable resource. In recent years, there has been escalating interest in the study of PEC valorization from the sacrifice of biomass, but only a few reviews have systematically and specifically addressed it. This review discusses the conversion mechanism of organics, the catalyst and system configuration, and the effect of other variables in detail based on different structures and types of biomass substrates. A brief outlook on the development of the field is outlined in the end as well, and PEC is expected to be an alternative low-carbon, energy-saving, multi-objective route to biomass valorization. [ABSTRACT FROM AUTHOR]

Various kinds of functional amines have been well synthesized by the reductive amination of carbonyl compounds for high-value pharmaceuticals, but they often suffer from complicated processes and low efficiency. In this study, we developed a facile strategy to achieve product diversity using iron-based nanoparticles, whose catalytic selectivity can be particularly controlled via specific combinations of active metals and carbonaceous matrixes in a simple way; over these catalysts, the main products completely switched from primary amines (>91.2%) to secondary imines (>92.3%) in a one-pot process, in accordance with the observed changes in chemical states (Fe0 to FexOy), particle size (9.3 to 63.2 nm), surface acidity (42.4 to 195.7 μmol g−1), and porosity (388.5 to 14.4 m2 g−1). By further analyzing the differences in reaction routes, the dehydration of nucleophilic amines with excess aldehydes was found to be the crucial step, accelerating the chemical equilibrium turned towards secondary imines. In addition, a wide range of substrates (>15 examples) were well tolerated by the prepared catalysts resulting in good to excellent yields (67.7–96.3%), and the catalytic stability was proven to be standard satisfactorily even after reusing up to five times, which was superior to commercial catalysts with noble or transition metals. More surprisingly, the magnetic properties exhibited by the iron cores allowed easy separation from aqueous systems. Overall, this strategy provides an applicable approach for the preparation of simple but highly efficient catalysts for switchable amination, which fills the knowledge gap on catalytic selectivity and exerts a positive impact on the industrial application. [ABSTRACT FROM AUTHOR]

The ammonia (NH3) synthesis industry is significant for many aspects of human progress and the global economy, especially in the fields of fertilizers, hydrocarbon-free energy carriers, and the production of emerging clean fuels. The world's energy for ammonia synthesis accounts for roughly 1–2% of social energy consumption. As an environmentally friendly and cheap raw material, N2 is abundant in nature. Therefore, the search for efficient catalysts that can convert N2 to NH3 under mild conditions with low energy consumption has always been a hot research topic in the field of catalysis. The conversion and utilization of renewable energy sources such as light and electricity, especially chemical energy, is of great importance to human society in terms of energy saving and environmental protection. One of the ways to reduce N2 to NH3 is the electrochemical nitrogen reduction reaction (e-NRR); however, the improvement of e-NRR activity is severely limited by the ultra-high chemical stability of N≡N bonds and the competition from the hydrogen evolution reaction (HER). The three main types of catalysts, metallic (metal complex) and non-metallic catalysts, together with natural biocatalysts, have been the target of development and improvement by researchers as suitable catalysts. In terms of photocatalytic N2 synthesis of ammonia, due to the relatively stable chemical properties of N2 molecules, it is difficult for traditional photocatalytic materials to generate the activity of reducing N2 molecules. Through continuous innovation and improvement of photocatalysts, researchers are able to increase the catalytic sites of catalysts and find suitable supporting materials to activate N2 molecules, which greatly improves the efficiency of photocatalytic N2 synthesis of ammonia. This review highlights the recent progress and development of photocatalysts and electrocatalysts for the synthesis of NH3 from N2, and briefly introduces the advantages of various catalysts and the comparison of synthesis efficiency. It is expected to provide a reference for the development of new processes that can produce high value-added chemicals. [ABSTRACT FROM AUTHOR]

Ionic liquids (ILs) as additives were used in the selective conversion of bio-based carbohydrates to 5-hydroxymethylfurfural (HMF) in this work. The effect of adding various imidazole-based ionic liquids with different anion structures on the production of HMF from fructose was firstly investigated in aqueous media. The presence of 15 wt% 1-butyl-3-methylimidazole chloride ([Bmim]Cl) ionic liquids in water with Fe2(SO4)3 as the homogeneous catalyst provided a more effective HMF synthesis compared to that without [Bmim]Cl addition. The enhanced HMF yield was mainly attributed to the fact that [Bmim]Cl might play a vital role in stabilizing the HMF molecule, which could thereby suppress side reactions involving HMF (e.g., its rehydration to levulinic acid or/and polymerization to humins). NMR and FTIR analyses suggested that such a stabilization effect stemmed from the interaction of [Bmim]Cl with the hydroxyl and aldehyde groups of HMF through hydrogen bonding. By performing the operation in a biphasic system (i.e., with the biomass-derived THF solvent as the organic phase and the addition of NaCl salt into water for improving HMF partition), the HMF yield over the Fe2(SO4)3 catalyst in the presence of the [Bmim]Cl additive could be further improved. The catalyst and ionic liquids were quite stable, and could be reused for more than five cycles with a consistent activity. A similar enhancement effect of [Bmim]Cl was also demonstrated in HMF synthesis with better yields from other biomass feedstocks or derivatives (including glucose, sucrose, cellobiose, inulin and starch) in aqueous media. [ABSTRACT FROM AUTHOR]

Novel catalytic material with high catalytic activity and hydrothermal stability plays a key role in the efficient conversion of levulinic acid (LA) to γ-valerolactone (GVL) in water. In this study, mixed oxides Al 2 O 3 -TiO 2 , Al 2 O 3 -MoO 3 and Al 2 O 3 -Co 3 O 4 were synthesized by co-precipitation using aqueous solution of NaOH as precipitant. Ru catalysts supported on mixed oxides were prepared by impregnation method and their catalytic performances were tested in the hydrogenation of LA to GVL on a fixed bed reactor. The physicochemical properties of the catalysts were characterized by XRD, H 2 -TPR, NH 3 -TPD, and BET techniques. The TiO 2 component significantly affected the acidity of the catalyst, and thus its catalytic activity for the GVL yield was affected. The desired product GVL with a yield of about 97% was obtained over the Ru/Al 2 O 3 -TiO 2 catalyst under mild conditions (WHSV = 1.8 h -1 , T = 80 °C). Moreover, the catalyst Ru/Al 2 O 3 -TiO 2 exhibited excellent thermal stability in the test period of time., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)