The development of high-efficiency and durable bifunctional electrocatalysts for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is critical for the widespread application of rechargeable zinc–air (Zn–air) batteries. This calls for rational screening of targeted ORR/OER components and precise control of their atomic and electronic structures to produce synergistic effects. Here, we report a Mn-doped RuO2 (Mn-RuO2) bimetallic oxide with atomic-scale dispersion of Mn atoms into the RuO2 lattice, which exhibits remarkable activity and super durability for both the ORR and OER, with a very low potential difference (ΔE) of 0.64 V between the half-wave potential of ORR (E 1/2) and the OER potential at 10 mA cm–2 (E j10) and a negligible decay of E 1/2 and E j10 after 250 000 and 30 000 CV cycles for ORR and OER, respectively. Moreover, Zn–air batteries using the Mn-RuO2 catalysts exhibit a high power density of 181 mW cm–2, low charge/discharge voltage gaps of 0.69/0.96/1.38 V, and ultralong lifespans of 15 000/2800/1800 cycles (corresponding to 2500/467/300 h operation time) at a current density of 10/50/100 mA cm–2, respectively. Theoretical calculations reveal that the excellent performances of Mn-RuO2 is mainly due to the precise optimization of valence state and d-band center for appropriate adsorption energy of the oxygenated intermediates.

Controlling the selectivity in single-step conversion of syngas to single aromatic hydrocarbon to enhance CO utilization is a big challenge. By adapting the reaction coupling methodology, which allows the precise control of C–C coupling reaction, we obtained a high selectivity of ∼70% of a single product, tetramethylbenzene (TeMB), in hydrocarbons, at total CO conversion of 37%. This was enabled by the reaction of H2-deficient syngas over a composite catalyst of physically mixed nanosized ZnCr2O4 and H-ZSM-5. The H-ZSM-5 employed in this work appeared as a coffin shape with short straight channels [010] along the b-axis that exhibit low molecular-diffusion resistance, resulting in high selectivity of aromatics, particularly TeMB. Due to selective methanol formation and enhanced molecular diffusion, we observed an aromatic vacancy created inside H-ZSM-5 pores, which boosts the transformation of olefins into aromatics, thus making the aromatic cycle dominant in a dual-cycle mechanism and giving a high yield of aromatics and TeMB. Furthermore, no catalyst deactivation was observed within 600 h of reaction time using H2-deficient syngas. Therefore, by rejecting the need for extra H2 addition into the syngas-to-aromatics (STA) reaction system, direct conversion of H2-deficient syngas derived from coal/biomass into TeMB makes an attractive industrial process.

The extensive emission of CO2 into the atmosphere due to the burning of fossil fuels has urged many countries to move toward decarbonized energy. Based on the concept of carbon neutrality, the European Union Emissions Trading System implemented the aviation carbon tax (ACT), which stimulated the rapid transformation in aviation fuels. To cope with the ACT and mitigate the CO2 emissions from the aviation industry, here, we present a promising route for the synthesis of precursors such as aromatics, alkyl benzenes, and naphthenes, which account for 40–50 vol % fraction of the kerosene-based aviation fuel, from waste CO2 or biomass-derived syngas. The ultra-high selectivity of single-ring aromatics (precursors for the kerosene-based aviation fuel) with a selective range of carbon chain numbers (C8–C12) was achieved (>80% in hydrocarbons at a reaction temperature of 275 °C) via the catalytic hydrogenation of CO2 or CO over a bifunctional catalyst (nano-sized ZnCr2O4/Sbx-H-ZSM-5). In situ diffuse reflectance infrared Fourier transform spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, gas chromatography–mass spectrometry, and reaction analysis revealed that the product distribution was controlled by thermodynamics and the formation of the aromatics followed an “aldol–aromatic” mechanism. The high selectivity of aromatics at the low reaction temperature (i.e., 275 °C) was attributed to the catalyst topology, the closed carbon chain aromatization reaction, and the presence of highly active oxygenated species in the hydrocarbon pool. For the first time, an asymmetric desorption behavior between the active oxygenate species and aromatic hydrocarbons over the ZnCr2O4/Sbx-H-ZSM-5 catalyst is reported with the help of integrated differential phase contrast scanning transmission electron microscopy, which made the reaction highly selective toward aromatics. This strategy gives a carbon-neutral route for the synthesis of kerosene-based aviation fuel precursors and will reduce the burden of the carbon tax on the aviation industry.

For the sustainability of the biodiesel industry, the selective glycerol dehydration to valuable acrolein using zeolite catalysts is a very important economic-sustainable route. For glycerol dehydration, the conventional micropore morphology of zeolites exhibits diffusion resistance to guest molecules through the longer channels and inhibits access to active acid sites, which leads to the formation of coke and reduces the stability and selectivity of the catalyst. In this work, we synthesized a highly crystalline nano H-ZSM-5 catalyst with short channels along the b-axis at different Si/Al ratios to investigate the effect of channel length and acidity on glycerol dehydration to acrolein. The H-ZSM-5 (Si/Al = 75) catalyst having a nano straight channel along the b-axis and medium acidity gave much higher conversion, stability, and selectivity to acrolein due to sufficient accessibility to active acid sites and rapid diffusion through the nanolength channels as compared to a commercial catalyst with longer channels.

Selectivity control in the single-step conversion of syngas to a single aromatic product is a big challenge. Here, we report an aldol-aromatic mechanism composed of aldol, phenolic, and aromatic cycles, that gave high selectivity >70% of a single product, tetramethylbenzene (TeMB) in hydrocarbons, at a reaction temperature as low as 275 °C. We evidently found the existence of oxygenated-aromatic compounds in the carbon pool, which remained active throughout the reaction and acted as key intermediates for the formation of the aromatics. The physical contact of ZnCr 2 O 4 with H-ZSM-5 exhibited a strong coupling effect that promoted surface diffusion of C 1 oxygenates (i.e., formaldehyde and methanol) from ZnCr 2 O 4 into H-ZSM-5 and transformed into aromatics via an aldol-aromatic reaction pathway, thus overcoming the most difficult step for first carbon−carbon bond formation. In addition, ZnCr 2 O 4 promoted the aromatics desorption by lowering the desorption activation energy and prevented the oversaturation of carbon pool species. Furthermore, it was found that a combination of thermodynamic equilibrium, surface methylation, and static repulsion are the key factors for giving high selectivity of TeMB in both carbon pool and final aromatics. This aldol-aromatic mechanism will open an efficient reaction pathway to upscale the process for selective aromatic synthesis in high yield from syngas.