Progress and opportunities related to the application of SSEs as central compartments for electrochemical catholyte-free CO₂RR have been described, with key parameters such as SSE type, product carrier, ion exchange membrane, and catalyst hydrophilicity, which affect the performance parameters, to produce a pure product with a high concentration.

Abstract

Research on electrocatalytic CO₂ reduction reaction (CO₂RR) has been growing rapidly owing to the urgent requirement of sustainable renewable energy. However, several obstacles hinder the application of liquid salt electrolytes in CO₂RR, such as high costs, low concentrations of the product, and low purity due to the separation process of the product. Solid-state electrolytes (SSEs) have been introduced as viable alternatives to liquid electrolytes and their salts to address this challenge. Here, we summarize the recently demonstrated studies and opportunities related to catholyte-free CO₂RR using SSEs. The recent studies are classified based on the product, including the CO₂RR electrolyzer performance. Different SSEs are briefly discussed to highlight the new opportunities in CO₂RR application. We also describe the basic operation parameter of the catholyte-free CO₂RR using SSE, which has been studied before as the key variable of the reactor. This review provides insights on minimizing the use of salt electrolytes for CO₂RR and reveal opportunities for using this technique to improve the efficiency of CO₂RR on a large scale. The exploration of utilizing solid-state electrolytes (SSE) on a scale-up production has been pursued to showcase their viability in integrating them into commercial CO₂RR technology.

Upon photon absorption, polynuclear gold complexes undergo metal-centered excitation, resulting in long-lived triplets with an increasing coordination number. This feature facilitates direct binding with substrates in the inner coordination sphere. The formed exciplex can undergo inner-sphere electron transfer to reduce or oxidize molecules, even in cases where the redox potentials do not match.

Abstract

Photo-induced electron transfer is a fundamental step in photochemical reactions, where light energy is used to drive chemical transformations. However, conventional outer-sphere single electron transfer mechanisms encounter multiple limitations, notably requiring redox potential matching between photocatalysts and substrates, thereby impeding the activation of non-activated carbon-halogen bonds. In this concept review, we present an elucidation of the photophysical and photochemical properties exhibited by polynuclear gold photocatalysts, with a particular emphasis on their inner-sphere single electron transfer mechanism. By exploring these intricate aspects, we endeavor to furnish readers with a more profound insight into the remarkable potential of polynuclear gold photocatalysts and the indispensable role played by inner-sphere electron transfer in the realm of photocatalysis.

A PdCu alloy catalyst loaded on a graphene oxide carrier was prepared through a simple liquid phase reduction method which greatly enhanced the catalytic performance with an ammonia yield of 1.62 mg h⁻¹cm⁻² and Faradaic efficiency of 38.2 % under the nitrate reduction ammonia synthesis (NO₃RR) reaction at an overpotential of −0.4 V. For the nitrogen reduction ammonia, the ammonia yield was 20.83 μg h⁻¹ cm⁻² with a Faradaic efficiency of 3.8 %.

Abstract

The conventional Haber-Bosch method for the ammonia synthesis process requires high temperature and pressure. Electrochemical synthesis of ammonia, an emerging ammonia synthesis technology, is a promising approach for sustainable ammonia production that is energy-efficient and free of greenhouse gas emissions. The design and development of high-performance catalysts are the keys to promoting the sustainable ammonia production process. This work synthesized a PdCu alloy catalyst loaded on a graphene oxide carrier through a simple liquid phase reduction method. Which greatly enhanced the catalytic performance with an ammonia yield of 1.62 mg h⁻¹cm⁻² and Faradaic efficiency of 38.2 % under the nitrate reduction ammonia synthesis (NO₃RR) reaction at an overpotential of −0.4 V. For the nitrogen reduction ammonia (NRR), the ammonia yield was 20.83 μg h⁻¹ cm⁻² with a Faradaic efficiency of 3.8 %. This study may provide a new idea for material design and promote ammonia synthesis development under ambient conditions.

The conversion of waste substrates into value added chemical products is a promising pathway to implement principles of circular economy in chemical industry and replace fossil feedstocks. To overcome the chemical complexity and heterogenous nature of waste feedstocks coupled processes are ideally suited. Implementing electrochemical steps enhances sustainability and opens novel reaction pathways.

Abstract

There is a strong initiative in chemical industry to replace fossil resources by alternative feedstocks and implement more sustainable production routes for chemicals. Waste feedstocks are especially appealing, considering the principles of circular economy. They exhibit, however, great structural complexity, and it is challenging to convert them into defined chemical products. To still enable the conversion of waste feedstocks into value added chemicals, coupled catalytic processes are a viable solution. A first reaction step transforms the waste substrate into more defined and soluble intermediates which are subsequently converted into value added chemicals, in a second reaction step. Electrochemical reactions are of great interest for such processes, especially in the context of sustainability, as they can be powered by electricity from renewable sources and enable unique chemical transformations. In this review different strategies for converting waste substrates into value added chemicals are addressed by using process couplings including electrochemical reactions. Such coupled processes are of great interest to enable the transformation of chemical industry towards sustainable processes following the principles of circular economy.

Stabilisation of metal species using hydroxyl-rich dealuminated zeolites is a promising method for catalysis. However, insights into the interactions between the hydroxyl groups in zeolite and noble metals and their effects on catalysis are not yet fully understood. Herein, comparative studies were conducted using Pt catalysts supported on hydroxyl-rich dealuminated Beta (deAl-Beta) and the pristine proton-form Beta (H-Beta) for catalytic oxidation of toluene. The findings suggest that during impregnation the Pt precursor (i.e., Pt(NH3)4(NO3)2) interacted with different sites on deAl-Beta and H-Beta, leading to the formation of supported Pt nanoparticles with different physicochemical properties. The resulting Pt/deAl-Beta exhibited improved activity and anti-coking ability than Pt/H-Beta in catalytic toluene oxidation. According to toluene-TPD, 1H NMR relaxation and in situ DRIFTS characterisation, the enhanced performance of Pt/deAl-Beta could be ascribed to (i) the active Pt-O sites stabilised by hydroxyl groups, which interact with toluene easily for conversion, and (ii) the acid-free feature of the deAl-Beta support, which avoids the formation of coke precursors (such as benzoate species) on the catalyst surface. Findings of the work can serve as the design guidelines for making effective supported metal catalysts using zeolitic carriers.

With resurgent interest in green hydrogen as a key element in the transition to a renewable-energy economy, developing efficient, earth-abundant, and low-cost catalysts for hydrogen evolution reaction (HER) is becoming increasingly important but is still very challenging. Herein, we report the synthesis of Co-doped Ni3C nanoparticles encapsulated in ultrathin carbon layers (CNCC) by in-situ thermal decomposition of organic-inorganic hybrid as high-performance HER electrocatalysts. Experimental and density functional theory studies evidence that the substantial high-index (113) surfaces in synergy with a few atomic carbon layers contribute significantly to the activity and stability, while the electronic structure of Ni3C is optimized through tuning the Co content to enhance the intrinsic kinetics for HER. The CNCC exhibits excellent HER activities with overpotentials at 10 mA cm−2 (η10) of 102 and 69 mV and Tafel slopes of 74 and 43 mV dec-1 in respective neutral and alkaline media along with a superior stability without noticeable decay up to 100 h. More importantly, the CNCC outperforms the benchmark Pt/C catalyst under high current density (> 38 mA cm-2) in an alkaline electrolyte, showing great potential for practical hydrogen production.

Bulky tri-isopropyl silyl (TIPS) substituents and deuterium atoms in the ligand design have been shown to enhance the site-selective oxidation of aliphatic C−H bonds and the epoxidation of C=C bonds in non-heme iron oxidation catalysis. In this work, a series of non-heme iron complexes were developed by combining TIPS groups and deuterium atoms in the ligand. These bulky deuterated complexes show a significant increase in catalytic performance. A broad range of substrates was oxidized with excellent yields, particularly, using [Fe(OTf)2((S,S)-TIPSBPBP-D4)] (1-TIPS-D4) via a fast or slow oxidant addition protocol, resulting in an overall improvement in catalytic performance. Notably, in the oxidation of the complex substrate trans-androsterone acetate, the use of a slow addition protocol and a lower catalyst loading of 1-TIPS-D4 resulted in significant increases in reaction efficiency. In addition, kinetic and catalytic studies showed that deuteration does not affect the catalytic activity and the secondary C-H site-selectivity but increased the catalysts’ lifetime resulting in higher conversion/yield. Accordingly, the yield of selectively oxidized secondary C-H products also increases with the overall yield by using the bulky deuterated iron complexes as catalysts. These catalytic improvements of the bulky deuterated complexes exemplify the enhanced design of ligands for homogeneous oxidation catalysis.

The development of low-cost nickel-based catalysts for direct and selective hydrogenation of 2-butyne-1,4-diol (BYD) to butane-1,4-diol (BAD) under mild conditions is an important and attractive target both in fundamental research and industrialization but remains a formidable challenge. The primary industrial production method for BAD synthesis is a two-step reaction route, which suffers from complicated catalysis conditions and high equipment costs. Herein, we develop a high-performance catalyst via a facile alcohol-treated strategy for highly selective BAD synthesis at moderate operation conditions. The as-synthesized NA-80E catalyst exhibits outstanding BAD selectivity of 98.82% and BYD conversion of 100% at 60 oC and 4 MPa, outperforming most reported results for BAD formation in a one-step process and even being comparable to those obtained by the two-step hydrogenation reaction route under much high temperatures and pressures. Crucially, we found that after facile alcohol (ethanol) treatment, an intriguing phenomenon of suppression of adjacent acid-assisted hydrogenolysis via extra acidic Al species at the NiO-Al2O3 interface is observed, contributing to the precise enhancement of BAD selectivity by inhibiting the production of butanol (BOL). This facile alcohol-treated method along with the revealed mechanism of blocked hydrogenolysis opens vast possibilities for designing high-performance and highly-selective hydrogenation catalysts.

In this work, the variation of the phosphorus content on the surface of vanadium-based bulk catalysts by atomic layer deposition is used to experimentally unravel its catalytic functionality in the selective oxidation of n-butane. The consecutive combustion of maleic anhydride is suppressed, due to a surface enrichment with phosphorus.

Abstract

Vanadium phosphates are established as the benchmark system for the selective oxidation of n-butane towards maleic anhydride. By varying the phosphorus content on the surface of three V-based catalysts with diverse performance, this study experimentally elaborates on the catalytic function of phosphorus. Contact time variation and cofeed studies revealed, that surface phosphates, deposited in sub-monolayers via atomic layer deposition, significantly contribute to an increased product selectivity. Furthermore, our results suggest that the phosphorus particularly suppresses the consecutive combustion of the (re-)adsorbed product. The recently introduced solid solution catalyst V_1-xNb_xOPO₄ with medium maleic anhydride selectivity could be tuned by the surface enrichment with phosphorus towards product selectivities of up to S_MAN=60 %, under optimized alkane-rich feed conditions. Therefore, PO_x-V_0.3Nb_0.7OPO₄ is introduced as promising catalyst, which is not based on vanadyl(IV) pyrophosphate, to access significantly higher MAN formation rates at increased alkane partial pressures of c _n-butane>10 %vol in n-butane oxidation.

Photoexcited 4-nitropyridine N-oxide biradical was found to catalyze the carbon radical generation from alkylboronic acids with blue LED irradiation without exogenous photocatalysts. With a wide range of readily available aliphatic boronic acids, including methyl boronic acid, the developed catalytic system allowed simple and robust applicability for alkylation, amination, and cyanation reactions.

Abstract

Herein we report a protocol for the generation of alkyl carbon radicals from alkylboronic acids wherein photoexcited 4-nitropyridine N-oxide biradical features a catalyst to promote the nucleo-homolytic substitution of boronic acids. With a wide range of readily available aliphatic boronic acids, including methyl boronic acid, the developed catalytic system demonstrates broad applicability for alkylation, amination, and cyanation.