Engineering the morphology and electronic structure of atomic cobalt-nitrogen-carbon catalyst with highly accessible active sites for enhanced oxygen reduction

The stabilization of non-precious metals as isolated active sites with high loading density over nitrogendoped carbon materials is essential for realizing the industrial application of single atom catalysts.However,achieving high loading of single cobalt active sites with greatly enhanced oxygen reduction reaction(ORR)activity and stability remains challenging.Here,an efficient approach was described to create a single atom cobalt electrocatalyst(Co SAs/NC)which possesses enhanced mesoporosity and specific surface area that greatly favor the mass transportation and exposure of accessible active sites.The electronic structure of the catalyst by the strong metal-support interaction has been elucidated through experimental characterizations and theoretical calculations.Due to dramatically enhanced mass transport and electron transfer endowed by morphology and electronic structure engineering,Co SAs/NC exhibits remarkable ORR performance with excellent activity(onset and half-wave potentials of 1.04 V(RHE)and 0.90 V(RHE),Tafel slope of 69.8 mV dec^(-1)and J_(k) of 18.8 mA cm^(-2)at 0.85 V)and stability(7 mV activity decay after 10,000 cycles).In additio n,the catalyst demonstrates great promise as an alternative to traditional Pt/C catalyst in zinc-air batteries while maintaining high performance in terms of high specific capacity of(796.1 mAh/g_(Zn)),power density(175.4 mW/cm^(2)),and long-term cycling stability(140 h).This study presents a facile approach to design SACs with highly accessible active sites for electrochemical transformations.

Rational design of palladium single-atoms and clusters supported on silicoaluminophosphate-31 by a photochemical route for chemoselective hydrodeoxygenation of vanillin

Chemoselective hydrodeoxygenation of vanillin is of great importance in converting biomass into high value-added chemicals.Herein,we describe a facile photochemical route to access palladium single atoms and clusters supported on silicoaluminophosphate-31(SAPO-31)as a highly active,chemoselective,and reusable catalyst for hydrodeoxygenation of vanillin.Characterizations by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy,extended X-ray absorption fine structure measurement,and CO-absorbed diffuse reflectance infrared Fourier transform spectroscopy reveal the atomically dispersed palladium single atoms and clusters are loosely bonded and randomly dispersed,without forming strong palladium-palladium metallic bonding,over the SAPO-31 support.This catalyst,with a full metal availability to the reactants,exhibits exceptional catalytic activity(TOF:3,000 h^(−1),Yield:>99%)in the hydrodeoxygenation of vanillin toward 2-methoxy-4-methylphenol(MMP)under mild conditions(1 atm,80°C,30 min),along with excellent stability,scalability(up to 100-fold),and wide substrate scope.The superior catalytic performance can be attributed to the synergistic effect of the positively charged palladium single atoms and fully exposed clusters,as well as the strong metal-support interactions.This work may offer a new avenue for the design and synthesis of fully exposed metal catalysts with targeted functionalities.

Single palladium atoms stabilized byβ-FeOOH nanorod with superior performance for selective hydrogenation of cinnamaldehyde

Atomically dispersed single atom catalysts represent an ideal means of converting less valuable organics into value-added chemicals of interest with high efficiency.Herein,we describe a facile synthetic approach to create defect-containingβ-FeOOH doped with isolated palladium atoms that bond covalently to the nearby oxygen and iron atoms.The presence of singly dispersed palladium atoms is confirmed by spherical aberration correction electron microscopy and extended X-ray absorption fine structure measurements.This single palladium atom catalyst manifests outstanding catalytic efficiency(conversion:99%;selectivity 99%;turnover frequency:2,440 h^(-1))in the selective hydrogenation of cinnamaldehyde to afford hydrocinnamaldehyde.Experimental measurements and density functional theory(DFT)calculations elucidate the high catalytic activity and the strong metal-support interaction stem from the unique coordination environment of the isolated palladium atoms.These findings may pave the way for the facile construction of single atom catalysts in a defect-mediated strategy for efficient organic transformations in heterogeneous catalysis.

Alkali ion-promoted palladium subnanoclusters stabilized on porous alumina nanosheets with enhanced catalytic activity for benzene oxidation

Catalytic C−H bond activation is one of the backbones of the chemical industry.Supported metal subnanoclusters consisting of a few atoms have shown attractive properties for heterogeneous catalysis.However,the creation of such catalyst systems with high activity and excellent anti-sintering ability remains a grand challenge.Here,we report on alkali ion-promoted Pd subnanoclusters supported over defectiveγ-Al_(2)O_(3) nanosheets,which display exceptional catalytic activity for C−H bond activation in the benzene oxidation reaction.The presence of Pd subnanoclusters is verified by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy,X-ray absorption spectroscopy,and X-ray photoelectron spectroscopy.This catalyst shows excellent catalytic activity,with a turnover frequency of 280 h^(−1) and yield of 98%,in benzene oxidation reaction to give phenol under mild conditions.Moreover,the introduction of alkali ion greatly retards the diffusion and migration of metal atoms when tested under high-temperature sintering conditions.Density functional theory(DFT)calculations reveal that the addition of alkali ion to Pd nanoclusters can significantly impact the catalyst’s structure and electronic properties,and eventually promote its activity and stability.This work sheds light on the facile and scalable synthesis of highly active and stable catalyst systems with alkali additives for industrially important reactions.

Synthesis of cobalt single atom catalyst by a solid-state transformation strategy for direct C-C cross-coupling of primary and secondary alcohols

Atomic engineering of single atom catalysts(SACs)with high-density available active sites and optimized electronic properties can substantially boost catalytic efficacy.Herein,we report a solid-state transformation strategy to access Co SACs by introducing Co species from commercial CO_(2)O3 powders into nitrogen-doped carbon support.The catalyst exhibited excellent catalytic activity,with a turnover frequency(TOF)of 2,307 h^(-1)and yield of 95%,in the direct C-C cross-coupling of benzyl alcohol and 1-phenylethanol(1 atm O2@80℃)to yield chaicone.Density functional theory(DFT)calculations demonstrate the coordination environment and electronic metal-support interaction impact the catalytic pathway.In particular,a wide substrate scope and a broad functional-group tolerance of this SAC were validated,and the employment of this strategy for large-scale synthesis was also shown to be feasible.This work might shed light on the facile and scalable synthesis of highly active,selective,and stable SACs for heterogeneous catalysis.

Engineering the atomic interface of porous ceria nanorod with single palladium atoms for hydrodehalogenation reaction

Tuning the electronic properties of single atom catalysts(SACs)between the central metal and the neighboring surface atoms has emerged as an efficient strategy to boost catalytic efficiency and metal utilization.Here we describe a simple and efficient approach to create atomically dispersed palladium atoms supported over defect-containing porous ceria nanorod containing palladium up to 0.26 wt.%.The existence of singly dispersed palladium atoms is confirmed by spherical aberration correction electron microscopy and extended X-ray absorption fine structure measurements.This catalyst shows excellent efficiency in hydrodehalogenation reactions at low H2 pressure under mild conditions,along with satisfactory recyclability and scalability.Density functional theory(DFT)calculations reveal that the high activity stems from the spatial isolation of palladium atoms and the modified electronic structure of palladium confined in defect-containing ceria nanorod.This work may lay the foundation for the facile creation of single atom catalysts within the synthetic community and shed light on the possibility for scale-up production.