The Development Of Beyond Mean Field State-to-state Microkinetics And Its Applications On Confinement Catalysis

In order to deeply understand the macroscopic chemical behavior of materials influenced by multiscale factors,it is necessary to comprehensively consider the chemical processes and influencing factors on different time and space scales.This gives rise to a great challenge to our material research at the present stage.With the rapid development of computer technology,the theoretical simulation strategy coupling first-principles calculation and mean field microkinetics has become an important means of cross-scale research of materials.Due to the shortcoming of mean field microkinetics for confinement catalysis with complex and locally inhomogeneous surface sites,beyond mean field state-to-state microkinetic framework is developed to study the intrinsic reaction behaviors of bimetal sites on mullite oxides,isolate sites with multiple atoms and double hydroxyls at noble metal nanoparticles,which gives some guidance for tuning the intrinsic reactivity of confinement systems under realistic experimental conditions.The details are followed:The beyond mean field state-to-state microkinetic framework is developed for confinement catalysis,where complex reaction sites are treated as a whole.The neighbor chemical environment of the surface species are considered to distinguish the different multi-molecular or atomic configurations on the restricted sites,which cpuld map the real reaction species under reaction conditions.At the same time,the method also can reduce the power of the steady-state equations and it is helpful for simplifying the solution of the equation groups.Using first-principles based microkinetic analysis,we conduct a comprehensive Ninvestigation on the NO oxidation processes along Mars-van Krevelen(Mv K)and Eley-Rideal(ER)mechanisms at surface oxygen and bimetal sites of Sm Mn₂O₅mullite,respectively,under experimentally relevant conditions.Mv K and ER mechanisms are also found to contribute to the high activity of pristine Sm Mn₂O₅in high and low temperature regions,respectively.The stability of NO^*species(NO binding with surface oxygen atoms)and dissociation of adsorbed O₂(O₂^*)are identified as the key factors affecting the reactivity of Mv K and ER mechanisms,respectively.Furthermore,we study the activity of surface(Ba,Sr and La)doped Sm Mn₂O₅.It is found that surface doping of Ba primarily destabilizes the nitrite species(NO^*)to promote NO oxidation performance via Mv K mechanism.Due to the stronger ability of O₂(O₂^*)dissociation along the ER route,Sr and La doped mullites are predicted to have greatly enhanced reaction activity in a wide temperature region.Our study gives insight into the NO oxidation ability of pristine and surface doped Sm Mn₂O₅that are beneficial for further optimization of mullite based catalyst performance.Coupling the competitive gaseous adsorptions and multiple reaction pathways via a state-to-state microkinetic formalism,we reveal CO oxidation mechanisms on small Pd_n(n=1,2,3,4)ensembles under realistic experimental conditions.It is found that reaction of O₂with pre-adsorbed CO on adjacent Pd sites is the dominant pathway at low temperature(denoted as pre-adsorbed CO oxidation pathway,or PCOP).Strong CO adsorption at Pd_nsites hinders the low-temperature reactivity and after detoxification,the binding ability of oxygen primarily controls the intrinsic CO oxidation activity.At even higher temperature,CO oxidation reaction primarily proceeds via the recombination of dissociated O atoms and CO(denoted as dissociated O₂pathway,or DO₂P)and enhanced oxygen adsorption can promotes the CO oxidation along DO₂P.Among different ensembles investigated,Pd dimer possesses the best low-temperature CO oxidation activity due to weaker CO poisonous effect,while tetramers outperform others at higher temperature.This work unravels the intrinsic activity of the catalyst on the microscopic scale and sheds lights on the ensemble engineering for maximizing its reactivity of the bimetal catalysts.Combining theoretical and experimental study,we focus on the decomposition behaviors of trimethylaluminum(TMA)and dimethylaluminum isopropoxide(DMAI)on different sites of Pt nanoparticles and find that Al O_xcan selectively encapsulate surface sites of Pt nanoparticles with DMAI as an ALD precursor.The selectivity originates from the preferential DMAI decomposition mechanism on double hydroxyl sites of Pt(111)facet,with the subsequent H₂O half cycle rapidly removing residual surface intermediates and regenerating hydroxyls as reaction sites for next cycles.Related microkinetic and experimental results confirm that by the substitution of one methyl in TMA with an isopropanol radical,DMAI as the precursor can preferentially coat Pt(111)facets and leave other sites intact through controlling the ALD deposition parameters,due to the more facile decomposition of DMAI at Pt(111).The substituent effect leads to strong Al-C bonding in DMAI and stable DMAI adsorption and it makes selective deposition of Al O_xpossible,which gives a clear guidance for ALD precursor design.In general,combining the theoretical and experimental study,our work gains insight into the selective growth mechanism and provides for the first time a feasible strategy to achieve the selective decoration Al O_xon Pt nanoparticles via ALD.