Kinetically rate-determining step modulation by metal-support interactions for CO oxidation on Pt/CeO_(2)

Rational design and performance promotion are eternal topics and ultimate goals in catalyst preparation.In contrast,trial–and–error is still the common method people take.Therefore,it is important to develop methods to intrinsically enhance the performance of catalysts.The most effective solutions are the one from a kinetic perspective based on clear knowledge of the reaction mechanism.This paper describes rate-determining step cognition and modulation to promote CO oxidation on highly dispersed Pt on CeO_(2).The different degrees of metal–support interactions due to variation of hydroxyl density of support could alter the structure of active species and the ability of oxygen activation apparently,further shift the rate-determining step from oxygen activation to oxygen reverse spillover kinetically.The transformation of rate-determining step could enhance the intrinsic activity significantly,and decrease the T_(50) approximately 140℃.The findings of this research exemplify the universal and effective method of performance elevation by rate-determining step modulation,which is promising for application in different systems.

Tuning dual-atom mediator toward high-rate bidirectional polysulfide conversion in Li-S batteries

An emerging practice in the realm of Li-S batteries lies in the employment of single-atom catalysts(SACs)as effective mediators to promote polysulfide conversion,but monometallic SACs affording isolated geometric dispersion and sole electronic configuration limit the catalytic benefits and curtail the cell performance.Here,we propose a class of dual-atom catalytic moieties comprising hetero-or homo-atomic pairs anchored on N-doped graphene(NG)to unlock the liquid–solid redox puzzle of sulfur,readily realizing Li-S full cell under high-rate-charging conditions.As for Fe-Ni-NG,in-depth experimental and theoretical analysis reveal that the hetero-atomic orbital coupling leads to altered energy levels,unique electronic structures,and varied Fe oxidation states in comparison with homo-atomic structures(FeFe-NG or Ni-Ni-NG).This would weaken the bonding energy of polysulfide intermediates and thus enable facile electrochemical kinetics to gain rapid liquid-solid Li_(2)S_(4)?Li_(2)S conversion.Encouragingly,a Li-S battery based on the S@Fe-Ni-NG cathode demonstrates unprecedented fast-charging capability,documenting impressive rate performance(542.7 mA h g^(-1)at 10.0 C)and favorable cyclic stability(a capacity decay of 0.016%per cycle over 3000 cycles at 10.0 C).This finding offers insights to the rational design and application of dual-atom mediators for Li-S batteries.

The Kinetics for Electrochemical Removal of Ammonia in Coking Wastewater

Electrochemical removal of ammonia is a new and effective method in coking wastewater.The reaction mechanism of ammonia removal was proved by stable polarization curve in this paper.First,the supposing of reaction steps of the electrode were proposed.And then reaction parameter of the electrode was measured by Tafel curve.Finally,the reaction mechanism was determined by quasi-equilibrium approach.The results showed that Cl2+H2O→HOCl+H++Cl was the rate-determining step,the calculated apparent transfer coefficient was uniform to the experimental value.

Eliminating nitrogen chemisorption barrier with single-atom supported yttrium cluster via electronic promoting effect for highly efficient ammonia synthesis

Nitrogen chemisorption is a prerequisite for efficient ammonia synthesis under ambient conditions,but promoting this process remains a significant challenge.Here,by loading yttrium clusters onto a single-atom support,an electronic promoting effect is triggered to successfully eliminate the nitrogen chemisorption barrier and achieve highly efficient ammonia synthesis.Density functional theory calculations reveal that yttrium clusters with abundant electron orbitals can provide considerable electrons and greatly promote electron backdonation to the N2 antibonding orbitals,making the chemisorption process exothermic.Moreover,according to the“hot atom”mechanism,the energy released during exothermic N2 chemisorption would benefit subsequent N2 cleavage and hydrogenation,thereby dramatically reducing the energy barrier of the overall process.As expected,the proof-of-concept catalyst achieves a prominent NH3 yield rate of 48.1μg·h^(−1)·mg^(−1)at−0.2 V versus the reversible hydrogen electrode,with a Faradaic efficiency of up to 69.7%.This strategy overcomes one of the most serious obstacles for electrochemical ammonia synthesis,and provides a promising method for the development of catalysts with high catalytic activity and selectivity.

Promoting ring-opening efficiency for suppressing toxic intermediates during photocatalytic toluene degradation via surface oxygen vacancies

Aromatic ring-opening process is well recognized as the rate-determining step for catalytic toluene degradation. In photocatalytic toluene degradation, the toxic intermediates w让h harmful effects may be generated. To clarify the precise reaction mechanism and control the toxic intermediates generation, a closely combined in situ DRIFTS and DFT calculation is utilized to address these important issues. We construct the BiOCl w让h oxygen vacancies (OVs) and reveal the structure of OVs. The defect level caused by oxygen vacancies could promote the light adsorption and charge separation, which further boosts the activation of ring-opening species and enhances the generation process of free radicals. The reaction energy barriers of four possible ring-opening processes on defective BiOCl (OVBOC) are all declined in comparison with perfect BiOCl (BOC). The existence of oxygen vacancies could smooth the ratedetermining step so the ring-opening efficiency of photocatalytic toluene degradation is highly increased. Most importantly, the methyl species would be further oxidized and tend to open the benzene-ring at benzoic acid on BOC while the ring would be broken at the benzyl alcohol on OVBOC. These results indicate that the toluene degradation pathway is shortened via the surface OVs, which enables the production of radicals with high oxidation capability for the accelerated chain scission of the ring-opening intermediates. Finally, the efficiency of the key ring-opening process could be enormously improved and toxic intermediates are effectively restrained. The present work could provide new insights into the design of high-performance photocatalysts for efficient and safe degradation of VOCs in air.

Glycerol aerobic oxidation to glyceric acid over Pt/hydrotalcite catalysts at room temperature

Glycerol(GLY) aerobic oxidation in an aqueous solution is one of the most prospective pathways in biomass transformation, where the supported catalysts based on noble metals(mainly Au, Pd, Pt) are most commonly employed. Herein, Pt nanoparticles supported on rehydrated MgxAl1-hydrotalcite(denoted as re-MgxAl1-LDH-Pt) were prepared via impregnation-reduction method followed by an in situ rehydration process, which showed high activity and selectivity towards GLY oxidation to produce glyceric acid(GLYA) at room temperature. The metal-support interfacial structure and catalyst basicity were modulated by changing the Mg/Al molar ratio of the hydrotalcite precursor, and the optimal performance was achieved on re-Mg6Al1-LDH-Pt with a GLY conversion of 87.6% and a GLYA yield of 58.6%, which exceeded the traditional activated carbon and oxide supports. A combinative study on structural characterizations(XANES, CO-FTIR spectra, and benzoic acid titration) proves that a higher Mg/Al molar ratio promotes the formation of positively charged Ptd+species at metal-support interface, which accelerates bond cleavage of a-C–H and improves catalytic activity. Moreover, a higher Mg/Al molar ratio provides a stronger basicity of support that contributes to the oxidation of terminal-hydroxyl and thus enhances the selectivity of GLYA. This catalyst with tunable metal-support interaction shows prospective applications toward transformation of biomass-based polyols.

Mechanisms of water oxidation on heterogeneous catalyst surfaces

Water oxidation,an essential step in photosynthesis,has attracted intense research attention.Understanding the reaction pathways at the electrocatalyst/water interface is of great importance for the development of water oxidation catalysts.How the water is oxidized on the electrocatalyst surface by the positive charges is still an open question.This review summarizes current advances in studies on surface chemistry within the context of water oxidation,including the intermediates,reaction mechanisms,and their influences on the reaction kinetics.The Tafel analyses of some electrocatalysts and the rate-laws relative to charge consumption rates are also presented.Moreover,how the multiple charge transfer relies on the intermediate coverage and the accumulated charge numbers is outlined.Lastly,the intermediates and rate-determining steps on some water oxidation catalysts are discussed based on density functional theories.