Search

Simultaneous transformation of CO2 and H2O into syngas (CO and H2) using solar power is desirable for industrial applications. Herein, an efficient photocatalyst based on double‐shelled nanoboxes, with an outer shell of hydroxy‐rich nickel cobaltite nanosheets and an inner shell of Cu2S (Cu2S@ROH‐NiCo2O3), is prepared via a multistep templating strategy. The high performance of Cu2S@ROH‐NiCo2O3 (7.1 mmol g−1 h−1 for CO; 2.8 mmol g−1 h−1 for H2) is attributed to the hierarchical hollow geometry and p–n heterojunction to promote light absorption and charge separation. Spectroscopic and theoretical analyses elucidate that the ROH‐NiCo2O3 surface enhances *CO2 adsorption and lowers energy barriers for CO2‐to‐CO. Therefore, modulating the hydroxy contents of ROH‐NiCo2O3 can achieve broad CO/H2 ratios from 0.51 to 1.24. This work offers in‐depth insights into adjustable syngas photosynthesis and generalized concepts of selective heterogeneous CO2 photoreduction beyond cobalt‐based oxides. [ABSTRACT FROM AUTHOR]

Based on detailed in situ attenuated total-reflection-surface-enhanced IR reflection absorption spectroscopy (ATR-SEIRAS) studies of the methanol oxidation reaction (MOR) on Ru/Pt thin film and commercial Johnson-Matthey PtRu/C, a revised MOR enhancement mechanism is proposed in which CO on Pt sites is irrelevant but instead Pt-Ru boundary sites catalyze the oxygen insertion reaction that leads to the formation of formate and enhances the direct reaction pathway. [ABSTRACT FROM AUTHOR]

Methanol serves as a versatile building‐block for various commodity chemicals, and the development of industrially promising strategies for its conversion remains the ultimate goal in methanol chemistry. In this study, we design a dual Cu−Cs catalytic system that enables a one‐step direct conversion of methanol and methyl acetate/ethanol into high value‐added esters/aldehydes, with customized chain length and saturation by leveraging the proximity and distribution of Cu−Cs sites. Cu−Cs at a millimeter‐scale intimacy triggers methanol dehydrogenation and condensation, involving proton transfer, aldol formation, and aldol condensation, to obtain unsaturated esters and aldehydes with selectivities of 76.3 % and 31.1 %, respectively. Cu−Cs at a micrometer‐scale intimacy significantly promotes mass transfer of intermediates across catalyst interfaces and their subsequent hydrogenation to saturated esters and aldehydes with selectivities of 67.6 % and 93.1 %, respectively. Conversely, Cu−Cs at a nanometer‐scale intimacy alters reaction pathway with a similar energy barrier for the rate‐determining step, but blocks the acidic‐basic sites and diverts the reaction to byproducts. More importantly, an unprecedented quadruple tandem catalytic production of methyl methacrylate (MMA) is achieved by further tailoring Cu and Cs distribution across the reaction bed in the configuration of Cu−Cs||Cs, outperforming the existing industrial processes and saving at least 15 % of production costs. [ABSTRACT FROM AUTHOR]

Achieving efficient catalytic conversion over a heterogeneous catalyst with excellent resistance against leaching is still a grand challenge for sustainable chemical synthesis in aqueous solution. Herein, we devised a single‐atom Pt1/hydroxyapatite (HAP) catalyst via a simple hydrothermal strategy. Gratifyingly, this robust Pt1/HAP catalyst exhibits remarkable catalytic selectivity and catalyst stability for the selective oxidation of C2–C4 polyols to corresponding primary hydroxy acids. It is found that the Pt−(O−P) linkages with strong electron‐withdrawing function of PO43− (Pt1−OPO43− pair active site) not only realize the activation of the C−H bond, but also destabilize the transition state from adsorbed hydroxy acids toward the C−C cleavage, resulting in the sharply increased selectivity of hydroxy acids. Moreover, the strong PO43−‐coordination effect provides electrostatic stabilization for single‐atom Pt, ensuring the highly efficient catalysis of Pt1/HAP for over 160 hours with superior leaching resistance. [ABSTRACT FROM AUTHOR]

Carbon monoxide (CO) is notorious for its strong adsorption to poison platinum group metal catalysts in the chemical industry. Here, we conceptually distinguish and quantify the effects of the occupancy and energy of d electrons, emerging as the two vital factors in d‐band theory, for CO poisoning of Pt nanocatalysts. The stepwise defunctionalization of carbon support is adopted to fine‐tune the 5d electronic structure of supported Pt nanoparticles. Excluding other promotional mechanisms, the increase of Pt 5d band energy strengthens the competitive adsorption of hydrogen against CO for the preferential oxidation of CO, affording the scaling relationship between Pt 5d band energy and CO/H2 adsorption energy difference. The decrease of Pt 5d band occupancy lowers CO site coverage to promote its association with oxygen for the total oxidation of CO, giving the scaling relationship between Pt 5d occupancy and activation energy. The above insights outline a molecular‐level understanding of CO poisoning. [ABSTRACT FROM AUTHOR]

Cu‐CHA is the state‐of‐the‐art catalyst for the Selective Catalytic Reduction (SCR) of NOx in vehicle applications. Although extensively studied, diverse mechanistic proposals still stand in terms of the nature of active Cu‐ions and reaction pathways in SCR working conditions. Herein we address the redox mechanism underlying Low‐Temperature (LT) SCR on Cu‐CHA by an integration of chemical‐trapping techniques, transient‐response methods, operando UV/Vis‐NIR spectroscopy with modelling tools based on transient kinetic analysis and density functional theory calculations. We show that the rates of the Reduction Half‐Cycle (RHC) of LT‐SCR display a quadratic dependence on CuII, thus questioning mechanisms based on isolated CuII‐ions. We propose, instead, a CuII‐pair mediated LT‐RHC pathway, in which NO oxidative activation to mobile nitrite‐precursor intermediates accounts for CuII reduction. These results highlight the role of dinuclear Cu complexes not only in the oxidation part of LT‐SCR, but also in the RHC reaction cascade. [ABSTRACT FROM AUTHOR]

Green and efficient synthesis of titanium‐containing molecular sieves is limited by the quantity of environmentally unfriendly additives and complicated synthesis procedures required. Oligomerization of Ti monomers into anatase TiO2 is the typical outcome of such procedures because of a mismatch between hydrolysis rates of Si and Ti precursors. We report a simple and generic additive‐free route for the synthesis of Ti‐containing molecular sieves (MFI, MEL, and BEA). This approach successfully reverses the formation of Ti oligomers to match hydrolysis rates of Ti and Si species with the assistance of hydroxyl free radicals generated in situ from ultraviolet irradiation. Moreover, fantastic catalytic performance for propene epoxidation with H2 and O2 was observed. Compared with the conventional hydrothermal method, this approach opens up new opportunities for high‐efficiency, environmentally benign, and facile production of pure titanium‐containing molecular sieves. [ABSTRACT FROM AUTHOR]

A bifunctional catalyst comprising CuCl2/Al2O3 and nitrogen‐doped carbon was developed for an efficient one‐pot ethylene oxychlorination process to produce vinyl chloride monomer (VCM) up to 76 % yield at 250 °C and under ambient pressure, which is higher than the conventional industrial two‐step process (≈50 %) in a single pass. In the second bed, active sites containing N‐functional groups on the metal‐free N‐doped carbon catalyzed both ethylene oxychlorination and ethylene dichloride (EDC) dehydrochlorination under the mild conditions. Benefitting from the bifunctionality of the N‐doped carbon, VCM formation was intensified by the surface Cl*‐looping of EDC dehydrochlorination and ethylene oxychlorination. Both reactions were enhanced by in situ consumption of surface Cl* by oxychlorination, in which Cl* was generated by EDC dehydrochlorination. This work offers a promising alternative pathway to VCM production via ethylene oxychlorination at mild conditions through a single pass reactor. [ABSTRACT FROM AUTHOR]

Abstract: A strategy is presented for making metal clusters encapsulated inside microporous solids selectively accessible to reactant molecules by manipulating molecular sieve size and affinity for adsorbed molecules. This expands the catalytic capabilities of these materials to reactions demanding high selectivity and stability. Selective hydrogen combustion was achieved over Pt clusters encapsulated in LTA zeolite (KA, NaA, CaA) in a propene‐rich mixture obtained from propane dehydrogenation, showing pore‐size dependent selectivity and coking rate. Propene tended to adsorb at channels or external surfaces of zeolite, interfering the diffusion of hydrogen and oxygen. Tailoring the surface of LTA zeolite with additional alkali or alkaline earth oxides contributed to narrowing zeolite pore size and their affinity for propene. The thus‐modified Pt@KA catalyst displayed excellent hydrogen combustion selectivity (98.5 %) with high activity and superior anti‐coking and anti‐sintering properties. [ABSTRACT FROM AUTHOR]

Achieving efficient catalytic conversion over a heterogeneous catalyst with excellent resistance against leaching is still a grand challenge for sustainable chemical synthesis in aqueous solution. Herein, we devised a single‐atom Pt1/hydroxyapatite (HAP) catalyst via a simple hydrothermal strategy. Gratifyingly, this robust Pt1/HAP catalyst exhibits remarkable catalytic selectivity and catalyst stability for the selective oxidation of C2–C4 polyols to corresponding primary hydroxy acids. It is found that the Pt−(O−P) linkages with strong electron‐withdrawing function of PO43− (Pt1−OPO43− pair active site) not only realize the activation of the C−H bond, but also destabilize the transition state from adsorbed hydroxy acids toward the C−C cleavage, resulting in the sharply increased selectivity of hydroxy acids. Moreover, the strong PO43−‐coordination effect provides electrostatic stabilization for single‐atom Pt, ensuring the highly efficient catalysis of Pt1/HAP for over 160 hours with superior leaching resistance. [ABSTRACT FROM AUTHOR]

Carbon monoxide (CO) is notorious for its strong adsorption to poison platinum group metal catalysts in the chemical industry. Here, we conceptually distinguish and quantify the effects of the occupancy and energy of d electrons, emerging as the two vital factors in d‐band theory, for CO poisoning of Pt nanocatalysts. The stepwise defunctionalization of carbon support is adopted to fine‐tune the 5d electronic structure of supported Pt nanoparticles. Excluding other promotional mechanisms, the increase of Pt 5d band energy strengthens the competitive adsorption of hydrogen against CO for the preferential oxidation of CO, affording the scaling relationship between Pt 5d band energy and CO/H2 adsorption energy difference. The decrease of Pt 5d band occupancy lowers CO site coverage to promote its association with oxygen for the total oxidation of CO, giving the scaling relationship between Pt 5d occupancy and activation energy. The above insights outline a molecular‐level understanding of CO poisoning. [ABSTRACT FROM AUTHOR]