Chinese Journal of Catalysis最新文献

The coordinated water in the Mn₄CaO₅ clusters in natural water oxidation center is believed to play an important role in promoting water oxidation. However, its specific role is unclear. In this work, based on a new manganese phosphate (Mn₂P₂O₇·3H₂O) with well-defined crystal surfaces (crystalline MnPi) and its amorphous counterpart (amorphous MnPi), the effects of coordinated water molecules on water oxidation have been systematically investigated. There are four coordinated water molecules on one Mn site, which is very rare and valuable to study relevant effects from water coordination. Unusually, the crystalline MnPi outperformed the amorphous MnPi in electrocatalysis. The exposed well-defined surface of the crystalline MnPi contains continuous Mn sites with multiple coordinated water molecules. The kinetics and thermodynamics of surface oxidation have been quantitatively studied based on the appealing catalyst platform. The interaction between adjacent Mn sites leads to a 3H⁺/2e dual site oxidation in crystalline MnPi, while this process is 2H⁺/1e single site conversion in amorphous MnPi. The higher level of charge neutralization of oxygen atoms from continuous H-bond network in crystalline MnPi is helpful for the Mn^II/III oxidation, which subsequently promotes water oxidation. This study provides valuable insight into the role of coordinated water molecules in initiating water oxidation in Mn-based catalytic systems.

Polyoxometalates (POMs) with well-defined molecular structures are sustainable and promising catalysts for reducing nitrogen to ammonia under ambient conditions. In this study, oxygen-vacancy-rich AgPW₁₁/Ag nanocube catalysts were synthesized via a one-pot method using POMs, reductants, and inducers. The oxygen-vacancy-rich AgPW₁₁/Ag heterojunction catalyst exhibited a significant ammonia yield as high as 46.02 ± 1.03 μg h^–1 mg^–1_cat. and faradaic efficiency of 34.07 ± 0.16% at a potential of –0.2 V (vs. RHE), maintaining stable catalysis for 32 h without decay and greatly outperforming the Ag catalyst. The excellent catalytic performance and mechanism were established using density functional theory calculations. The robust interaction between the d orbitals of the Ag atom in AgPW₁₁^12e and π* orbitals of N₂ activates the adsorbed N₂ and promotes the conversion of the first protonation process *N₂ to *N–NH (the potential determination step). This study provides a new avenue for designing stable Ag-based catalysts for nitrogen fixation.

Heterogeneous hydrogenation with supported metal catalyst is one of the efficient methods for producing fine chemicals. Hydrogenation reactions for fine chemical production often use reactants with more than one unsaturated bond or involve cascade multiple-step reactions, facing the dilemma of activity and selectivity. The dual-site or multi-site catalysts have been employed to solve this dilemma, but the entanglement at different sites generally cannot improve selectivity without reducing activity. In this review, we will introduce recent progresses in the construction of dual-site supported metal catalysts with division of active site, which may break the tradeoff between activity and selectivity in selective hydrogenation considering that each active sites can be modulated separately without causing the property variation of other sites. In addition, such catalysts contribute to the basic understanding of their structure-activity relationship and provide a theoretical basis for the development of efficient hydrogenation catalysts for fine chemical production.

Directional construction of crystalline/amorphous (c/a)-phosphosulfide heterostructures with exceptional intrinsic activity through a facile strategy is challenging. In this study, we synthesized q-CoPS nanorods with a unique c/a-CoPS core-shell heterostructure through the ‘gas-phase phosphorus vulcanization-quenching' treatment. This work also innovatively masters the regulation of the initial quenching temperature to alter the c/a ratio of the CoPS nanorods. Surprisingly, with increasing initial quenching temperature, the area of the amorphous CoPS shell gradually increases. Density functional theory calculations reveal that the Co sites at the c/a-heterointerface, as the difunctional c/a-interface active site, effectively optimize the kinetics of the hydrogen evolution reaction (HER) and hydrazine oxidation reaction (HzOR). As anticipated, q-CoPS/CF requires an overpotential of only 90 mV at a current density of 1000 mA cm^–2 for the alkaline HER, which is much lower than that required using the state-of-the-art Pt/C catalyst. Additionally, q-CoPS/CF achieves a current density of 1000 mA cm^–2 at only 0.06 V in the HzOR. Overall, this work proposes an efficient strategy for developing a bifunctional electrocatalyst with a unique c/a-heterostructure to address future energy needs.

Herein, perylenetetracarboxylic acid (PTA) nanosheets with anisotropic charge migration driven by the formed internal electric fields are synthesized through a facile hydrolysis-reassembly process. Strategically, a Z-scheme heterojunction with free-flowing interfacial charge transfer and spatially separated redox centers is constructed based on the distinct photogenerated electrons and holes accumulation regions of PTA nanosheets by in-situ introducing BiVO₄ quantum dots (BQD) and nanosized Au. The optimized BQD/PTA-Au exhibits a ca. 6.4-fold and 4.8-fold enhancement in H₂O₂ production rate and apparent quantum yield at 405 nm compared with pristine PTA, respectively. The exceptional activities are attributed to the cascade Z-scheme charge transfer followed the matched charge migration orientation, as well as the Au active sites for accelerating 2e^– oxygen reduction pathway induced by superoxide radicals, as unraveled by electron paramagnetic resonance, in-situ irradiated X-ray photoelectron spectroscopy and in-situ diffuse reflectance infrared Fourier transformation spectroscopy. This work provides a strategy to design an efficient Z-scheme system towards solar-driven H₂O₂ production.

Valorization of biomass and plastics is an urgent assignment to achieve the goal of carbon neutrality. Hydrodeoxygenation using bimetallic catalysts with distinct active sites is one of the most effective approaches to producing fuels and chemicals via C–O/C–C bonds hydrogenolysis and hydrogenation. Rational design of bimetallic catalysts has been progressed in recent studies owing to the understanding of synergy and strong mutual interaction between metal nanoparticles and metal oxide species. Thus, activity of bimetallic catalysts has been further improved, and the chemoselectivity for suppression of C–C bond dissociation and the regioselectivity among different C–O bonds, which have less been achieved before, are realized in the hydrodeoxygenation reactions. The catalytic performances, catalyst structures, and reaction mechanisms are directly compared and discussed in details based on the C–O bond cleavage using glycerol and 1,2-propanediol hydrogenolysis as model reactions over Ir-, Pt-, and Ru-based bimetallic catalysts. Finally, application of these bimetallic catalysts to conversion of lignocellulose-derived feedstocks, carbonyl compounds, and typical plastic of polycarbonates is introduced.

Methylenedianilines (MDA) are widely used as intermediates in the production of polyurethanes and polyisocyanurates. The current routes for the production of MDA offer only limited control of the isomer ratio (4,4’/(2,4’+2,2’)), with 4,4’-MDA being the most valuable isomer. While 2,4’-MDA is also marketed, significant added value could be unlocked upon further steering the production towards 4,4’-MDA. We here show that zeolites such as Beta can selectively isomerize 2,4’-MDA towards the desired 4,4’-MDA via a bimolecular mechanism, in an aniline background. While several acid zeolites were found to be active isomerization catalysts, MCM-68 (MSE topology) in particular combines high isomerization activity with efficient shape-selective suppression of the formation of unwanted 2,2’-MDA and oligomers. The origin of this shape-selectivity was studied, highlighting the crucial role of the acid site location in the pore confinement of MSE zeolites.

Owing to the rapid recombination of photogenerated electron-hole pairs with strong Coulomb interactions, the photocatalytic activity of metal-free conjugated polymers is often unsatisfactory. This article reports a simple method for incorporating carbon dots (CDs) into highly crystalline covalent triazine frameworks (CTFs) by directly heating a pretreated mixture of 1,4-dicyanobenzene, CDs, and alkali metal salts in air. The resultant photocatalyst exhibits a H₂O₂ production rate, solar-to-chemical conversion efficiency, and apparent quantum yield of 2464 μmol h^–1 g^–1, 0.9% at full spectrum, and 13% at 500 nm, respectively, surpassing most reported photocatalysts. The results of this study reveal that CDs can serve as hole extractors to efficiently drive exciton dissociation and can offer active sites for water oxidation reactions. This study is also the first to observe that alkali metal ions can interact with the carboxylic acid groups on the surface of CDs during synthesis to enhance the hole-extraction ability of CTFs, thereby accelerating photocatalytic H₂O₂ production. This study provides insights into the rational design of highly efficient CDs-based photocatalysts.

Owing to the multiple proton-coupled electron transfer steps involved in the electrochemical carbon dioxide reduction reaction (CO₂RR), single-atom catalysts (SACs) are ideal platforms for studying such complex chemical reaction processes. The structural simplicity and homogeneity of SACs facilitate the understanding of the structure-performance relationship and reaction mechanisms of the CO₂RR. Operando attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) is a valuable tool to identify the dynamic intermediate transformation processes in the CO₂RR occurring on SACs and to study the impact of local reaction environments on the CO₂RR performance. This article reviews operando ATR-SEIRAS and its key applications in the SAC-catalyzed CO₂RR. The review briefly introduces the surface enhancement mechanism of electrochemical in situ infrared spectroscopy, formation mechanisms of the C1 and C2 products, function of operando ATR-SEIRAS in investigating the mechanisms of single-/dual-atom catalysts in converting CO₂/CO to C1 and C2 products, and methods of using spectroscopic information to determine the interfacial H₂O and local pH at the electrode. Finally, the review provides perspectives on the future development of operando ATR-SEIRAS.

The surface structures of heterogeneous catalysts significantly impact catalytic performance, especially for structure-sensitive reactions. In this study, we employed surface techniques such as low-energy ion scattering spectroscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy with CO as a probe (CO-FTIR) to investigate the surface dynamics of Rh/Al₂O₃ catalysts for propane dehydrogenation (PDH). We observed a notable induction process for PDH on Rh/Al₂O₃ catalysts, marked by significant variations in propane conversion, methane, and propylene selectivities. These changes were attributed to substantial coke formation. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy) and CO-FTIR revealed the coexistence of Rh nanoparticles, clusters, and single atoms on the surface. Through various dynamic quasi in-situ characterizations, we found that coke preferentially covered Rh clusters, thereby inhibiting C–C bond breaking and methane formation. Meanwhile, Rh single atoms were less affected by coke coverage and remained exposed as active and selective sites for PDH, favoring propylene production. This work underscores the sensitivity of PDH to the sizes of Rh species, with isolated Rh single atoms promoting propylene formation.