High-temperature treatment to engineer the single-atom Pt coordination environment towards highly efficient hydrogen evolution

Development of high-performance and cost-effective catalysts for electrocatalytic hydrogen evolution reaction(HER)play crucial role in the growing hydrogen economy.Recently,the atomically dispersed metal catalysts have attracted increasing attention due to their ultimate atom utilization and great potential for highly cost-effective and high-efficiency HER electrocatalyst.Herein,we propose a hightemperature treatment strategy to furtherly improve the HER performance of atomically dispersed Ptbased catalyst.Interestingly,after appropriate high-temperature treatment on the atomically dispersed Pt0.8@CN,the Pt species on the designed N-doped porous carbon substrate with rich defect sites can be re-dispersed to single atom state with new coordination environment.The obtained Pt0.8@CN-1000 shows superior HER performance with overpotential of 13 m V at 10 m A cm^(-2)and mass activity of 11,284 m A/mgPtat-0.1 V,much higher than that of the pristine Pt0.8@CN and commercial Pt/C catalyst.The experimental and theoretical investigations indicate that the high-temperature treatment induces the restructuring of coordination environment and then the optimized Pt electronic state leads to the enhanced HER performances.This work affords new strategy and insights to develop the atomically dispersed high-efficiency catalysts.

Catalytic Combustion of Methane over High Copper-Loading ZSM-5 Catalysts

Two series of Cu/ZSM-5 catalysts, loading from 5 to 20 wt% CuO, were prepared by the deposition-precipitation and impregnation methods, respectively. The catalysts prepared by the impreg- nation method showed better catalytic performances than those prepared by the deposition-precipitation method and the increase of copper loading favored methane conversion. 20Cu（I）/ZSM-5 had the highest activity with T90% of 746 K, and for 20Cu（D）/ZSM-5, T90% was as high as 804 K. The characterization of X-ray diffraction （XRD）, temperature-programmed reduction （TPR）, temperature-programmed desorption （TPD）, and X-ray photoelectron spectroscopy （XPS） revealed that the dispersion of copper species could be improved by using the deposition-precipitation method instead of the impregnation method, but the fraction of surface CuO, corresponding to active sites for methane oxidation, was larger on 20Cu（I）/ZSM-5 than 20Cu（D）/ZSM-5. The results of Pyridine-Fourier transform infrared spectrum （Py-FT-IR） showed that a majority of Lewis acidity and a minority of Brфnsted acidity were present on Cu/ZSM-5 catalysts. 20Cu（I）/ZSM-5 presented more Lewis acid sites. The number of Lewis acid sites changed significantly with preadsorption of oxygen. Adsorption of methane and oxygen on acid sites was observed. The properties of Cu/ZSM-5 catalysts were correlated with the activity for methane oxidation.

Nested Metal Catalysts:Metal Atoms and Clusters Stabilized by Confinement with Accessibility on Supports

Supported catalysts that are important in technology prominently include atomically dispersed metals and metal clusters.When the metals are noble,they are typically unstablesusceptible to sinteringespecially under reducing conditions.Embedding the metals in supports such as organic polymers,metal oxides,and zeolites confers stability on the metals but at the cost of catalytic activity associated with the lack of accessibility of metal bonding sites to reactants.An approach to stabilizing noble metal catalysts while maintaining their accessibility involves anchoring them in molecular-scale nests that are in or on supports.The nests include zeolite pore mouths,zeolite surface cups(half-cages),raft-like islands of oxophilic metals bonded to metal oxide supports,clusters of non-noble metals(e.g.,hosting noble metals as single-atom alloys),and nanoscale metal oxide islands that selectively bond to the catalytic metals,isolating them from the support.These examples illustrate a trend toward precision in the synthesis of solid catalysts,and the latter two classes of nested catalysts offer realistic prospects for economical large-scale application.

Facile synthesis of C_(3)N_(4)-supported metal catalysts for efficient CO_(2) photoreduction

Facile synthesis of photocatalysts with highly dispersed metal centers is a high-priority target yet still a significant challenge.In this work,a series of Co-C_(3)N_(4) photocatalysts with different Co contents atomically dispersed on g-CaN4 have been prepared via one-step thermal treatment of cobalt-based metal-organic frameworks(MOFs)and urea in the air.Thanks to the highly dispersed and rich exposed Co sites,as well as good charge separation efficiency and abundant mesopores,the optimal 25-Co-C_(3)N_(4),in the absence of noble metal catalysts/sensitizers,exhibits excellent performance for photocatalytic C0_(2) reduction to CO under visible.light irradiation,with a high CO evolution rate of 394.4μmol·g^(-1)·h^(-1),over 80 times higher than that of pure g-C_(3)N_(4)(4.9μmol·g^(-1)·h^(-1)).In:addition,by this facile synthesis strategy,the atomically dispersed Fe and Mn anchoring on g-C_(3)N_(4)(Fe-C_(3)N_(4) and Mn-C_(3)N_(4))have been also obtained,indicating the reliability and universality of this strategy in synthesizing photocatalysts with highly dispersed metal centers.This work paves a new way to develop cost-effective photocatalysts for photocatalytic C0_(2) reduction.

Dehydrogenation activities of highly dispersed transition metal oxides on NaY zeolite

Highly dispersed α-Fe_2O_3/NaY,NiO/NaY,and CuO/NaY catalyst systems were pre- pared by impregnation method.Dispersion thresholds of the transition metal oxides on NaY' zeolite were determined by XRD phase analysis.The dispersion capacities of the transition metal oxides on NaY zeolite are much lower than that estimated on the basis of a closed packed monolayer in the micro pores.The catalytic activity and selectivity of the highly dispersed oxide catalyst systems for ethylben- zene and cyclohexane dehydrogenation reactions were reported.

Polymer-chelation approach to high-performance Fe-Nx-C catalyst towards oxygen reduction reaction

Pyrolyzed Fe-Nx-C with atomically dispersed Fe-Nxsites are hailed as the most promising alternative to the noble metal Pt-based catalysts towards oxygen reduction reaction(ORR). However, the conventional micropore-confinement synthetic approach usually causes the insufficient utilization of active sites and mass transport resistance as the sites are located inside the micropore. We herein report a polymerchelation strategy to directly disperse the Fe-Nxactive sites onto the carbon surface. The N-rich monomer was in-situ polymerized on the carbon support and then chelated with Fe. The strong Fe-N chelating interaction is crucial to suppress Fe aggregation when undergoing the high-temperature pyrolysis. Due to the enriched surface sites, hierarchically porous structure and excellent conductivity of carbon support,the optimal catalyst(denoted as Fe-Nx-C@C-900) exhibits impressive ORR activity of onset and half-wave potential of 1.02 and 0.87 V, respectively, superior to the Pt/C benchmark.

Effects of Ce on catalytic combustion of methane over Pd-Pt/Al_2O_3 catalyst

Activity and stability of 1%Pd-0.2%Pt/Al2O3 and 1%Pd-0.2%Pt/0.6%Ce/Al2O3 catalysts prepared by impregnation method for catalytic combustion of methane in air were investigated. The catalysts before and after reaction were characterized by BET, CO chemisorption, XRD and XPS techniques. Results showed that the presence of Ce significantly increased the activity and thermal stability of the Pd-Pt/Al2O3 catalyst towards methane combustion, which could be attributed to more highly-dispersed active PdO particles over the Pd-Pt/Ce/Al2O3 catalyst surface as well as the retarded sintering of PdO and the maintained oxidized state of surface Pd during the combustion process in the presence of Ce.

Atomic Fe-N4 sites on electrospun hierarchical porous carbon nanofibers as an efficient electrocatalyst for oxygen reduction reaction

Porous carbon materials doped with atomically dispersed metal sites(ADMSs)are promising electrocatalysts for oxygen reduction reaction(ORR)electrocatalysis.In this work,we fabricated hierarchical porous nitrogen-doped carbon nanofibers with atomically dispersed Fe-N4 sites by carbonization of electrospinning iron-based metal-organic frameworks(MOFs)/polyacrylonitrile nanofibers for ORR electrocatalysis.Remarkably,the re sultant carbon nanofibers with atomically dispersed FeN4 sites exhibit extraordinary electrochemical performance with an onset potential of 0.994 V and a halfwave potential of 0.876 V in alkaline electrolyte,comparable to the benchmark commercial Pt/C catalyst.The high catalytic performance is originated from the unique hierarchically porous 1 D carbon structure and abundant highly active atomically dispersed Fe-N4 sites.