Improving the ammonia synthesis activity of Ru/CeO_(2) through enhancement of the metal–support interaction

The metal–support interactions induced by high-temperature hydrogen reduction have a strong influence on the catalytic performance of ceria-supported Ru catalysts. However, the appearance of the strong metal–support interaction leads to covering of the Ru species by Ce suboxides, which is detrimental to the ammonia synthesis reaction that requires metallic species as active sites. In the present work, the interaction between Ru and ceria in the Ru/CeO_(2) catalyst was induced by NaBH_(4) treatment. NaBH_(4) treatment enhanced the fraction of metallic Ru, proportion of Ce^(3+), content of exposed Ru species, and amount of surface oxygen species. As a result, a larger amount of hydrogen species would desorb by the H_(2)-formation pathway and the strength of hydrogen adsorption would be weaker, weakening the inhibition effect of the hydrogen species on ammonia synthesis. In addition, the strong electronic metal–support interaction aids in nitrogen dissociation. Consequently, Ru/CeO_(2) with NaBH_(4) treatment showed higher ammonia synthesis rates than that with only hydrogen reduction.

Strong metal‐support interaction boosting the catalytic activity of Au/TiO_(2) in chemoselective hydrogenation

Gold catalysts have been reported as highly effective catalysts in various oxidation reactions.However,for chemoselective hydrogenation reactions,gold‐based catalysts normally show much lowercatalytic activity than platinum group metals,even though their selectivities are excellent.Here,wereport that the chemoselective hydrogenation activity of 3‐nitrostyrene to 3‐vinylaniline overAu/TiO_(2)can be enhanced up to 3.3 times through the hydrogen reduction strategy.It is revealedthat strong metal‐support interaction,between gold nanoparticles(NPs)and TiO_(2)support,is introducedthrough hydrogen reduction,resulting in partial dispersion of reduced TiOx on the Au surface.The partially covered Au not only increases the perimeter of the interface between the gold NPs andthe support,but also benefits H_(2)activation.Reaction kinetic analysis and H_(2)‐D2 exchange reactionshow that H_(2)activation is the critical step in the hydrogenation of 3‐nitrostyrene to 3‐vinylaniline.Density functional theory calculations verify that hydrogen dissociation and hydrogen transfer arefavored at the interface of gold NPs and TiO_(2)over the hydrogen‐reduced Au/TiO_(2).This study providesinsights for fabricating highly active gold‐based catalysts for chemoselective hydrogenationreactions.

A Review on Metal-support Interaction in Automotive Catalysts

TWC-equipped exhausts are widely used in gasoline-fueled vehicles to meet stringent emission regulations. The main components in TWCs are precious metals such as palladium (Pd), platinum (Pt), and rhodium (Rh) as the active component, and inorganic oxides such as γ-alumina (Al 2 O 3 ), ceria (CeO 2 ), zirconia (ZrO 2 ) and ceria-zirconia (CeO 2-ZrO 2 ) are used as the support. Interaction of precious metals and support plays an important role in the thermal stability and catalytic performance of TWCs. The support can improve the dispersion of precious metals and suppress the sintering of precious metals at high temperature. In the same, precious metals can also enhance the redox performance and oxygen storage capacity of support. This paper reviews the reaction phenomenon and mechanism of precious metals (Pt, Pd, Rh) and supports such as Al 2 O 3 , CeO 2-based composite oxides.

Single‐atom catalysts on metal‐based supports for solar photoreduction catalysis

Metal atoms atomically dispersed on an inorganic metal‐based support compose a unique category of single atom catalysts(SACs)and have important applications in catalytic photoreduction reactions,including H_(2) evolution reaction,CO_(2) reduction reaction,and N_(2) reduction reaction.In this minreview,we summarized the typical metal‐support interaction(M‐SI)patterns for successful anchoring of single‐atom metals on metallic compound supports.Subsequently,the contribution of the dispersed single metal atoms and M‐SI to photocatalytic reactions with improved activity,selectivity,and stability are highlighted,such as by accelerating charge transfer,regulating band structure of the support,acting as the reductive sites,and/or increasing catalytic selectivity.Finally,some challenges and perspectives of future development are proposed.We anticipate that this minireview will be a beneficial supplement for a comprehensive perception of metal‐based material supported SACs and their application in heterogeneous photo‐reductive catalysis.

Toward enhanced alkaline hydrogen electrocatalysis with transition metal‐functionalized nitrogen‐doped carbon supports

Superior catalyst supports are crucial to developing advanced electrocatalysts toward heterogeneous catalytic reactions.Herein,we systematically investigate the role of transition metal‐functionalized N‐doped carbon nanosheets(M‐N‐C,M=Mn,Fe,Co,Ni,Cu,Mo,and Ag)as the multifunctional electrocatalyst supports toward hydrogen evolution/oxidation reactions(HER/HOR)in alkaline media.The results demonstrate that all the M‐N‐C nanosheets,except Cu‐N‐C and Ag‐N‐C,can promote the alkaline HER/HOR electrocatalytic activity of Pt by accelerating the sluggish Volmer step,among which Mn plays a more significant role.Analyses reveal that the promotion effect of M‐N‐C support is closely associated with the electronegativity of the metal dopants and the relative filling degree of their d‐orbitals.For one,the metal dopant in M‐N‐C with smaller electronegativity would provide more electrons to oxygen and hence tune the electronic structure of Pt via the M‐O‐Pt bonds at the interface.For another,the transition metal in M‐N4 moieties with more empty d orbitals would hybridize with O 2p orbitals more strongly that promotes the adsorption of water/hydroxyl species.The results demonstrate the conceptual significance of multifunctional supports and would inspire the future development of advanced electrocatalysts.

Synthesis of Pd nanoparticles supported on CeO_2 nanotubes for CO oxidation at low temperatures

Developing efficient supported Pd catalysts and understanding their catalytic mechanism in CO oxidation are challenging research topics in recent years.This paper describes the synthesis of Pd nanoparticles supported on CeO2 nanotubes via an alcohol reduction method.The effect of the support morphology on the catalytic reaction was explored.Subsequently,the performance of the prepared catalysts was investigated toward CO oxidation reaction and characterized by Nitrogen sorption,X-ray diffraction,X-ray photoelectron spectroscopy,transmission electron microscopy,and CO-temperature-programmed desorption techniques.The results indicated that the catalyst of Pd on CeO2 nanotubes exhibits excellent activity in CO oxidation at low temperatures,due to its large surface area,the high dispersion of Pd species,the mesoporous and tubular structure of the CeO2-nanotube support,the abundant Ce3＋,formation of Pd–O–Ce bonding,and enhanced metal–support interaction on the catalyst surface.

Modulating metal-support interaction between Pt_(3)Ni and unsaturated WOx to selectively regulate the ORR performance

Tuning strong metal-support interaction between Pt-based alloys and metal oxides is an effective strategy for modulating the performance of oxygen reduction reaction(ORR).Herein,Pt_(3)Ni alloy anchored on WO_(x) with different content of oxygen vacancies is synthesized,and the effect of unsaturated WO_(x) on ORR activity/stability is revealed.Electrochemical results indicate that ORR activity is positively correlated with oxygen vacancy concentration,while durability presents the opposite trend.Density functional theory(DFT)calculation results suggest that controlling the content of oxygen vacancies can usefully adjust the charge redistribution between Pt_(3)Ni and WO_(x),which can optimize the adsorption/activation of reactants,thus obtaining good ORR activity.This study uncovers the effect of unsaturated WO_(x) on ORR performance for Pt-based alloys and provides a promising strategy to design efficient and stable ORR catalysts.

Top-down synthesis strategies: Maximum noble-metal atom efficiency in catalytic materials

Top‐down synthesis has been used to prepare catalytic materials with nanometer sizes,but fabricating atomically dispersed metal catalysts remains a challenge because surface single metal atoms are prone to aggregation or coalescence.A top‐down strategy is used to synthesize atomically dispersed metal catalysts,based on supported Ag nanoparticles.The changes of the geometric and electronic structures of the Ag atoms during the top‐down process are studied using the in situ synchrotron X‐ray diffraction technique,ex situ X‐ray absorption spectroscopy,and transmission electron microscopy.The experimental results,coupled with the density functional theory calculations,demonstrate that the electronic perturbation of the Ag frontier orbitals,induced by the Ag‐O interactions at the perimeter of the metal‐support interface,is the driving force of the top‐down process.The top‐down synthesis has two important functions:to increase the number of catalytic active sites and to facilitate the study of complex reaction mechanisms(e.g.,formaldehyde oxidation)by developing single‐site model catalysts.

Incorporating Sulfur Atoms into Palladium Catalysts by Reactive Metal–Support Interaction for Selective Hydrogenation

Developing highly active and selective catalysts for the hydrogenation of nitroarenes,an environmentally benign process to produce industrially important aniline intermediates,is highly desirable but very challenging.Pd catalysts are generally recognized as active but nonselective catalysts for this important reaction.Here,we report an effective strategy to greatly improve the selectivity of Pd catalysts based on the reactive metal–support interaction.

Catalytic performance enhancement by alloying Pd with Pt on ordered mesoporous manganese oxide for methane combustion

Ordered mesoporous Mn2O3 (meso‐Mn2O3) and meso‐Mn2O3‐supported Pd, Pt, and Pd‐Pt alloy x(PdyPt)/meso‐Mn2O3; x = (0.10?1.50) wt%; Pd/Pt molar ratio (y) = 4.9?5.1 nanocatalysts were prepared using KIT‐6‐templated and poly(vinyl alcohol)‐protected reduction methods, respectively.The meso‐Mn2O3 had a high surface area, i.e., 106 m2/g, and a cubic crystal structure. Noble‐metalnanoparticles (NPs) of size 2.1?2.8 nm were uniformly dispersed on the meso‐Mn2O3 surfaces. AlloyingPd with Pt enhanced the catalytic activity in methane combustion; 1.41(Pd5.1Pt)/meso‐Mn2O3gave the best performance; T10%, T50%, and T90% (the temperatures required for achieving methaneconversions of 10%, 50%, and 90%) were 265, 345, and 425 °C, respectively, at a space velocity of20000 mL/(g?h). The effects of SO2, CO2, H2O, and NO on methane combustion over1.41(Pd5.1Pt)/meso‐Mn2O3 were also examined. We conclude that the good catalytic performance of1.41(Pd5.1Pt)/meso‐Mn2O3 is associated with its high‐quality porous structure, high adsorbed oxygen species concentration, good low‐temperature reducibility, and strong interactions between Pd‐Pt alloy NPs and the meso‐Mn2O3 support.

A palladium single-atom catalyst toward efficient activation of molecular oxygen for cinnamyl alcohol oxidation

Selective aerobic oxidation of alcohols under mild conditions is of great importance yet challenging,with the activation of molecular oxygen(O2)as a crucial capability of the catalysts.Herein,we demonstrate that an Al2O3-supported Pd single-atom catalyst leads to higher activity and selectivity compared to Pd nanoparticles for the oxidation of cinnamyl alcohol.The Al2O3 support used in this study is rich in coordinately unsaturated Al3+sites,which are apt for binding to Pd atoms through oxygen bridges and present a distinct metal-support interaction(MSI).The suitable MSI then leads to a unique electronic characteristic of the Pd single atoms,which can be confirmed via X-ray photoelectron spectroscopy,normalized X-ray absorption near-edge structure,and diffuse reflectance Fourier transform infrared spectroscopy.Moreover,this unique electronic state is proposed to be responsible for its high catalytic activity.With the help of in-situ UV-vis spectra and electron spin resonance spectra,a specific alcohol oxidation route with O2 activation mechanism is then identified.Active oxygen species behaving chemically like singlet-O2 are generated from the interaction of O2 with Pd1/Al2O3,and then oxidize the partially dehydrogenated intermediates produced by the adsorbed allylic alcohols and Pd atoms to the desired alkenyl aldehyde.This work provides a promising path for the design and development of high-activity catalysts for aerobic oxidation reactions.

Graphdiyne oxide substrate-enhanced peroxidase-mimicking performance of Ru nanoparticles with physiological pH preference

Modulating electronic structure of metal nanoparticles via metal–support interaction has attracted intense interest in the field of catalytic science.However,the roles of supporting substrates in regulating catalytic properties of nanozymes remain elusive.In this study,we find that the use of graphdiyne oxide(GDYO)as the substrate for self-terminating growth of Ru nanoparticles(Ru@GDYO)endows the peroxidase-like activity of Ru nanoparticles with intrinsic physiological pH preference and natural horseradish peroxidase(HRP)comparable performance.Ru nanoparticles electrolessly deposited onto GDYO possess a partially oxidized electronic structure owing to limited charge transfer between Ru and GDYO,contributing to the intrinsic physiological pH preference of the peroxidase-mimicking nanozyme.More importantly,the substrate GDYO plays an influential factor in enhancing catalytic activity,that is,the activity of Ru@GDYO is much higher than that of Ru nanoparticles deposited on other carbon substrates including graphene oxides and graphdiyne.To demonstrate the application of Ru@GDYO nanozyme in neutral solutions,we employ Ru@GDYO with nicotinamide adenine dinucleotide(NAD+)-dependent dehydrogenases in physiological conditions to realize a sustainable cascade reaction by means of forming continuous NAD^(+)/dihydronicotiamide adenine dinucleotide(NADH)recycling.Our finding represents a promising perspective on designing high-performance peroxidase-mimicking nanozymes with broader applicability,raising fundamental understanding of structure–activity relationship,and investigating new applications of nanozymes in biological systems.

Wet-milling synthesis of immobilized Pt/Ir nanoclusters as promising heterogeneous catalysts

Being a typical state of the art heterogeneous catalyst,supported noble metal catalyst often demonstrates enhanced catalytic properties.However,a facile synthetic method for realizing large-scale and low-cost supported noble metal catalyst is strictly indispensable.To this end,by making use of the strong metal-support interaction(SMSI)and mechanochemical reaction,we introduce an efficient synthetic route to obtain ultrafine Pt and Ir nanoclusters immobilized on diverse substrates by wet chemical milling.We further demonstrate the scaling-up effect of our approach by large-scale ball-milling production of Pt nanoclusters immobilized on TiO_(2)substrate.The synthesized Pt/Ir@Co_(3)O_(4)catalysts exhibit superior oxygen evolution reaction(OER)performance with only 230 and 290 mV overpotential to achieve current density of 10 and 100 mA·cm^(-2),beating the catalytic performance of Co_(3)O_(4)supported Pt or Ir clusters and commercial Ir/C.It is envisioned that the present work strategically directs facile ways for fabricating supported noble metal heterogeneous catalysts.