Theoretical Study on the Adsorption and Decomposition of Methanol over the Pt-Mo(111)/C Surface

29卷8期结构化学(JIEGOU HUAXUE)Vol. 29, No.82010. 8Chinese J. Struct Chem.1159-1168Theoretical Study on the Adsorptionand Decomposition of Methanolover the Pt-Mo(111 )/C SurfaceWANG Yi-Wei*LI Lai-CaibWANG Xin°TIAN An-Min°"(Department of Foundation Medical, Luzhou Medical College, Luzhou 646000, China)"(Department of Chemistry, Sichuan Normal Universit; Chengdu 610066,6 China)。(Departinent of Chemistry, Sichuan Universit, Chengdu 610064, China)ABSTRACTThe density functional theory (DFT) and self-consistent periodic calculation wereused to investigate the methanol adsorption on the Pt-M0(111)/C surface. The adsorption energies,equilibrium geometries and vibration frequencies of CHzOH on nine types of sites on thePt- Mo(111)/C surface were predicted and the favorite adsorption site for methanol is the top-Pt site.Both sites of valence and conduction bands of doped system have been broadened, which arefavorable for electrons to transfer to the cavity. The possible decomposition pathway wasinvestigated with transition state searching and the calculation results indicate that the O -H bond isfirst broken, and then the methanol decomposes into methoxy. The activation barrier of 0-H bondbreaking with Pt -Mo catalyst is only 104.8 kJ mol", showing that carbon supported Pt Mo alloyshave promoted the decomposition of methanol. Comparing with the adsorption energies of CHzOHon the Pt(111)/C surface and that of CO, the adsorption energies of CO are higher, and Pt(111)/C isliable to be oxidized and loses the activity, which suggests that the catalyst Pt -Mo(111)C is in favorof decomposing methanol and has better anti-poisoning ability than Pt(111)/C.Keywords: methanol, Pt-M0(11)/C surface, DFT, electronic structure1 INTRODUCTIONfuel clls'). Direct methanol fuel cells (DMFC)differ from the other types in that hydrogen isFuel cell is one of the very promising technologiesobtained from the liquid methanol, elininating thethat receive increasing attention because of its abilityneed for a fuel reformer3.4. DMFC is a promisingto increase the overall energy efficiency'". Simplytransportable power source. The use of DMFC toput, a fuel cell is an electrochemical device that con-- power vehicles has been the subject of intense de-verts hydrogen and oxygen into electricity withoutvelopment efforts in recent years due to the signi-combustion'2. The general design of most fuel cellsficant advantages of zero emissions of pollutants andis similar except for the electrolyte. The five mainhigher efficiency which these systems offer4. Thetypes of fuel cells, as defined by their electrolyte, arecharacteristics are of particular importance in largealkaline fuel cells, proton exchange membrane fuelmetr中国煤化工m intense atmos-cells, phosphoric acid fuel cells, molten carbonatepheriYHCN M H G° of autobilse.fuel cells, direct methanol fuel cells, and solid oxideHowever, tnere are two major problems aboutReccived 10 October 2009; accepted 18 January 2010①Correspodig author. E mail: laica2009@126.comWANG Y. W. et al: Theoretical Study on the Adsorption and1160Decomposition of Methanol over the Pt-Mo(111)/C SurfaceNo.8DMFC. One is the electro .catalytic activity of me~highest performancefls!. Gotz's experiment has alsothanol at anode and it is low; the other, the penetra-pointed out that the modified electronic structure oftion of methanol from anode to cathode, is quitePuMo alloy surpasses the pure Pt catalystl6. Insevere. Therefore, to prepare a kind of anode catalystGrgur's opinion, there are numerous 0 and OH:with high electro catalytic activity for methanolmatches, which are effective to oxidate Co on theoxidation is very urgent5~n. A kind of anode ca-metal Pt. Indeed, Pt-Mo crystal is one of the effica-talyst with high electro-catalytic activity, steadycious alloy catalysts given by Anderson!. Timocapability and low cost must be prepared in theand his co-workers undertook the first principlespresent studies of DMFC. At present, the develop-quantum mechanism calculations to study thement of catalysts has concerned mainly the pre-adsorption of atomic H and 0 on the(111) surface ofparation and physico- chemical characterization of aPtNi alloy. It turmed out that the oxygen atom bindsPt catalyst with a lower concentration of activemore strongly on the PtNi alloy tban on purespecies on carbon supports for the electrochemicalplatinum and the positions of both elements (H andreduction of oxygen and the electro-oxidation of0) are more localized on the alloy surfacel18. How-methanol, respectively. Owing to the absence ofever, the microcosmic mechanism of the adsorp-activity, the dominances of kinetics on the anodetion over Pt- -Mo(111)/C suface still remains unclearcatalyst are not all shownlS~ 9. The anode catalystand few relevant theoretical studies have beenplays such an important role in DMFC, as a result,performed. To make a better understanding of thesenew carbon supported Pt-alloy catalysts arereactions, we investigated the methanol adsorptiondeveloped in order to increase the efficiency ofon the Pt -Mo(111)/C surface using the first-prin-electrodest, ". It is only known that platinum is aciples density functional theory (DFT) and self-con-catalyst with high reaction for all kinds of reactions,sistent periodic calculation. Moreover, the adsorp-but now Pt has been found to be the best electro-tion of carbon monoxide (CO) on the Pt -Mo(1111catalytic for the oxygen reduction reaction (ORR)surface, the anti-poisoning ability of bimetallicbecause of its higher electro-catalytic activity andcatalysts and the change of electronic structure arestability. Some researchers attributed it to the Pt 5ddiscussed in detail.band vacancy that leads to the stronger Pt-O2interactiol!2l and also some others have reported2 COMPUTATIONAL MODELSthat pure Pt has high ability to bind oxygen surfaceAND METHODSspecies, and thus, alloy is a way to lower the PtOchemisorption energyI13!. Ordering and disorderingLattice constant of Pt- Mo catalysts is 0.3918 nml!9),in the alloy bulk also play an important role inwhich is chosen to determine the optimal com-enhancing the surface catalytic activity of oxygenposition of Pt and Mo in the alloy system; we adoptreduction reaction, for example doping Ni, Fe andthe way as mentioned above. Considering precisionMo, and different doping elements are of differentand efficiency, we build Pt- -Mo(111) surface on thateffests4.. These may give us so many importantbasis and select 3x3 super-cell to research thismessages to adjust the properties of metal Pt, tosystem. Zhang and his co-workers2o0l have checkedselect the appropriate doping elements, etc. It hasthe same self-consistent periodic calculation to studybeen sbown that the carbon supported Pt- M (M = Ni,heof methanol over中国煤化工Fe, Mo) aloys have been tested as methanol-tolerantthe3 Liul2 has alsooxygen reduction catalysts in experiment, andseleJTYHc N M H EGmethanol adsopoamong the Pt- Mo/C aloys in 1:3, 1:1 and 3:1 Pt:Motion on the Au(111) surface, which is consistent withatomic ratios, the Pt-Mo/C 1:1 catalyst shows thethe experiment values.2010 Vol. 29结构化学(JIEGOU HUAXUE)Chinese_ J._ Struct._ Chem.1161Carbon carrier is superposed by numerous layersfamiliar to us(26- -28), but there, are few theoreticalparallel to the base level. Carbon atom of each layerstudies on the adsorption of these gases overforms a normal hexagon and three proximate atomsPt(111)/C surface. First of all, the equilibriumare linked by covalent bond to become a netlikegeometries of CHzOH on four adsorption sites of top,plane which can stretch in plane. We adopt one kindhcp, fcc and bridge on the Pt(111)/C surface areof cartbon calculation models and the length ofC Coptimized, and Ends on four adsorption sites are 81.1,bond is 0.142 nm. The similar model was used for57.9, 76.6 and 62.3 kJ mol'", respectively. It in-sulfur supported metal surface discussed by Mayl2).dicates that the adsorption favors to occur at the topAll calculations have been performned using DMol'site. The adsorption energy of CHgOH on Pt(111)/Ccodel23, 24] as implemented in Accelrys Materialsis relatively higher than that of some metals, whichStudio 4.0. The generalized gradient approximationshows that Pt is helpful to promote the decompo-(GGA) with Perdew-Wang (PW91)25] exchange-sition of CH3OH and becomes a useful catalyst ofcorrelation functional is selected in the DFTdirect methanol fuel cells (DMFC); on the other side,calculations. Effective Core Potentials (ECPs) havesome experiments reported that metal Pt is likely tobeen employed for all-electron calculations, wherebe oxidated when carbon monoxide (CO) is presentthe effect of core electrons is subtituted by a simplein the fuel gas, referred as CO poisoning[29 -34. Herepotential including some degree of relativisticwe continue to compute the adsorption energies ofeffects. This technique is computationally inexpen-CO on four adsorption sites of top, bcp, fcc andsive with good approximation for elements withbridge on the Pt(111)/C surface, which are 126.7,atomic numbers more than 21. The convergence164.74, 137.19 and 158.12 kJ mo1"', respectively,criteria of optimization were 0.001 eV/A and 0.001and the results are in good consistence with theA for energy gradient and atomic displacement,experimental findings between 120 and 160 kJrespectively. The charge density has been convergedmor!Ds, 36. Comparing the adsorption energy ofto1 x 10%, which corresponds to a total energy con-CHzOH on Pt(111)/C surface and that of CO, thevergence of1 x 105 eV. Fine grid mesh points areadsorption energy of CO is higher and Pt(11)/C isemployed for the matrix integrations. The adsorptionfavorable to be oxidized and loses the activity, whichenergies, equilibrium geometries, and vibrationalcause the properties of DMFC to reduce simulta-frequencies of CH3OH on nine possible types ofneously. About the mechanism of CHzOH adsorp-sites on the Pt- -Mo(111)/C surface are predicted.tion over Pt -Mo alloy catalyst, some scholars haveAdsorption cnergy values are computed byobtained the same conclusion that CHzOH is cataly-Esa = Emechanol + Er.Moc- EmthoPn-MorCzed by the double function mechanism, namely,where the subscripts methanol and Pt- Mo/C denotethanks to the double function mechanism of metalsthe energies of CH3OH and Pt- Mo/C respectivelyPt and Mo and along with the dehydrogenationbefore adsorption. Furthermore, the subscript me-occurring over the atom Pt to form some oxo-speciesthanol-Pt-Mo/C refers to the energy of the adsorbedlike OHg on the atom Mo, the reaction is expressed assystem.H2O+ Mo - + Mo-OH + H'e^Pt-CO + Mo-OH - + Pt+ Mo + CO2+H+3 RESULTS AND DISCUSSIONMetal Mo can promote the oxidation of poisonousintermediatel37,38] Tn eparch a mmre reasonable ca-3.1 Process of CH;OH adsorptiontalyst中国煤化工he P(M111Con the Pt(11)/C surfacesurfacMHCNMHGTheoretical study on the gas molecule (such as CO,3.2 Adsorption model, energy andCO2, CHOH, etc.) chemisorption on pure Pt(111) isvibrational frequency analysisWANG Y. W. et al: Theoretical Study on the Adsorption and1162Decomposition of Methanol over the Pt-M0(111)/C SurfaceNo. 8Gome et al.B9) have found that CH3OH can befree CHyOH are in agreement with the availableadsorbed on the most stable Cu(111) surface byexperimental results, indicating that the methods andtheoretical study. In this work, we optimized themodes we have chosen are reasonable. The structureequilibrium geometries of CHzOH on nine types ofof CH3OH molecule changes during the process ofsites of Pt-Mo(111)/C surface using the mode ofadsorption, that is, the O -H and 0 C bonds areoxygen-ending adsorption in which the 0-C bond ofelongated, and their vibrational frequency is red-original structure situates vertically over the Cu(111)shifed in the equilibrium adsorption models. Mean-surface, as shown in Fig. 1. To study the structuralwhile, the 0-H bond is activated greatly. Among thechange of adsorbed CHzOH is our major work. Theadsorption of CH3OH on nine types of sites of Pt-first step is to compute the free CHzOH molecule,Mo(11)C surface, the change of structural para-and then compares our results with the experimentalmeter over the top-Pt site is very distinct from thatvalues. From Table 1, the computational results ofof the others.Side viewTop view◎❽FIg. 1. Left) side view of the Pt-M0(11)/C surface with the unit lttice, (Right) ilustration ofadsorption sites on the Pt-Mo11/C surface in the top view (1 top-Pt; 2 top-Mo; 3 bridge-Pt; 4 biridge-Mo; 5 bcp-Pt2Mo; 6 bcp-PtM02; 7 fcc-Pt2Mo; 8 fc-PtMo2; 9 bridg-PtMo)Table 1. Geometrical Parameters, Vibrational Frequenciesand Adsorption Energies on the Pt-M0111)/C SurfaceAdsorptionR(0-H)/am R(C-0) /mm R(C-H)y(O-H)cm' (C-0)1cm’ Bascuow/ Ewrcosit/nmkJ mor')(kJ-mor')Top-Pt0.09820.14430.11053617.1981.7105.029.4Top-Mo0.14423622.6980.994.267.6Bridg-Pt3635.9984.677.349.6Bridgc-Mo0.09800.14410.11043726.41022.6462.0Bridge-PtMo 0.09823628.7983.685.852.5hep.PrMo3718.51007.97292.3hcp-PMor0.09813689.2中国煤化工8.fc-PtMo3620.7MHC NMH Go.6fc-PIMo23630.3CH0H0.09690.14270.11023750.71054.6(expet,)*(0.0945$3)(0.14253) 。(0.1094 (3682)(1026**The experimental values from references 43 and 44 are given in parcotheses.2010 Vol. 29.结构化学(JIEGOU HUAXUE)Chinese J. Struct Chem.1163Taking an example of adsorption on the top-Pt site,we know the product CO not only pollutes thethe bond length of 0 -H is 0.0013 nm longer thanatmosphere but also poisons the catalyst easily.that of the ftee one, and the C-0 bond is elongatedTherefore, we need to improve the catalyst in orderby 0.0015 nm; however, the bond length of C -H hasto enbance its anti-poisoning ability. Ji and hischanged only 0.0003 nm. On the other hand, theco-workers'4o have used DFT to investigate thevibrational frequency has changed more: theadsorption of CO on the Mo doped Pt(111) surface,decrease of 133.6 and 72.9 cm- for 0 -H and C-0,showing that the barrier on PtMo is indeed lowerrespectively. The red shift reveals that the cor-than that of the pure for CO oxidation and has higherresponding bond is weakened, and 0 -H has theactivity of PtMo. As a continuation of our inves-strongest active degree and tends to break. Thetigation, the adsorption energies of CO on nine typeschange of the other three modes also has the similarof sites on carbon supported Pt-M0(111) surfacetendency, namely, the intensities of 0 -H and C-0have been summarized in Table 1, all of which arebonds are weakened together.lower than that of CO on carbon supported P(11)From Table 1, we can find out that the favorablesurface. Furthermore, except the bridge-Mo site, theadsorption sites for methanol is the top-Pt site byother Eads-Co are lower than the Eade-CH3OH of cor-comparing the adsorption energies of methanol onresponding sites (Fig. 2). For the top-Pt site with thenine types of sites. These results are consistent withhighest adsorption energy of methanol, the anti-that of Shuhong Liu ec.", and we can see that it ispoisoning ability of Pt-M0(11)/C is improved grea-reasonable to obtain the equilibrium geometries bytly, and the result agrees well with a lot of theoreticalfixing the crystal substrate; furthermore, it seemsstudies which have found that CO is localized at thethat the restructuring of surface is so weak that thetop-Pt sitel41~43]. It indicates that the catalyst Pt-adsorption energies and structures fail to be afected.Mo111)/C that is in favor of decomposing methanolThe decomposition reaction of methanol over thehas better anti-poisoning ability than Pt(111])C.platinum clusters to Co and H2 is endothermal; as110.一一 Ead-ch3oh100 ------ Ead-co90.8070503001234.5678910sites 0r中国煤化工THCNMHG1 top-Pt, 2 top-Mo, 3 bridge-Pt, 4 bridge-Mo, 5 bridge-PtMo,6 bcp-Pt2Mo, 7 hep-PtMoz, 8 fe-Pt,Mo, 9 fc-PtMo2Fig. 2。Comparison of Eds CuoH and Ear-co on nine types of sites of the Pt-Mo0111)/C surfaceWANG Y. W. et al: Theoretical Study on the Adsorption and1164Decomposition of Methanol over the Pt-M0111)/C SurfaceNo, 83.3 Elctronic structurethe crystal substrate mainly by the two pairs ofFrom the Mulliken charge analysis in Table 2, wesolitary electrons of atom O. As we know, thcan find that the methanol in doping system iselectronic structures of Pt and Mo are 5d6s' andobviously changed compared with the carbon sup-4dSs，respectively. Obviously, the mumber ofported pure Pt metal. For adsorption systems,electrons of Mo d electronic-orbital is fewer thamethanol has taken the positive electrical charge. Itthat of atom Pt and atom Mo replaces the formerindicates that the charge transfers from CHzOH tosites of Pt, resulting in the increase of vacancy of dthe crystal substrate in the adsorption. Generallyelectronic-orbital of catalyst that induces the twospeaking, both C and 0 atoms adopt the hybrid ofpairs of solitary electrons of atom 0 which maysp' in free methanol molecule. Moreover, atom 0prefer to transfer to the d orbital of atom Pt. On thetakes two pairs of solitary electrons. The highestother hand, for methanol molecule, the Pz orbital ofoccupied molecular orbitals (HOMO) of metbanolatom 0 is matchable with the d2 orbital of atom Pt,molecule belong to the bonding-orbital, which is inand stronger chemical bonding forms between themthe flfilling state, the component of which mainlywhich can bring on the stronger chemical actioncomes from the two pairs of solitary electrons ofamong the whole adsorption system. Therefore, thisatom O. Owing to the o* orbital of the lowestdoping system investigated has higher adsorptionoccupied molecular orbital (LOMO) of methanolenergy than the pure one. In the work, the highestmolecule, which has so high energy, it hardly gainsadsorption energy of methanol over carbon suppor-charge from the surface and also its componentted Pt-M0(111) is 105.0 kJ-mor", but that overmainly comes from the two pairs of solitary elec-carbon supported pure Pt(111) is only 63.7trons of atom O. The methanol molecule reacts onkm1"4.Table 2. Muliken Population Analysis for CHzOH/Pt-M11)(111) Adsorption System (unit: a.u.)Adsorption site99w9HCIBO__TopPt-0.4510.293-0.0180.0840.083 .0.0850.076Tp-Mo-0.4540.2910.0830.072Bridgc-Pt-0.4570.2890.0820.063Bridge-Mo-0.4880.2800.021Bridge-PtMo-0.455bhp-Pt2Mo-0.4790.288-0.0170.042bep-PMoz0.2810.034fcc-PrMo0.284fec-PtMo2-0.476.0.2830.038Free-0.5550.2670.0880.0680.0690.000Density states (DOS) of carbon supported Pt(111)the doped system has been broadened, thus inducingand Pt-M0(111) are shown in Fig. 3. It suggests thatthe energy of electrons, which is favorable for elec-the form of doping energy-level is mainly attributedtron transfer fom reducing agent to the conductionto the 4d orbital of Mo atom. We can find the DOSband of metal.of doped system shift to lower energy, and it is clear3.4 Dissociation of metbanol overthat doping elements can promote the reaction ratethe Pt-Mo(111)/C surfacein the oxidation step, namely, the catalytic activitywe find out the tophas been advanced. As shown in Fig. 3b, when Mosite中国煤化工s favorable forwas doped in the Pt/C catalyst, the Fermi level of thehe :JYHCNMH G. The top-Pt sitecluster model moved to right both sites of partialadsorption state can be used as the reactant of dis-energy-level of valence band and conduction band ofsociation process of methanol. We continue to2010 Vol. 29结构化学(JIEGOU HUAXUE)Chinese J. Struct. Chem.1165compute the adsorption of CH2O and H on thewhich is in co-adsorption state to optimize is reason-Pt-Mo(111)/C surface and it turns out that the bestable, and the stable geometry is obtained as theadsorption site of CH3O is the bridge-Pt site and thatproduct of dissociating methanol over the Pt-of H is the fcc-PtMo site. Accordingly, puttingMo(111)/C surface, as shown in Fig.4.CHzO and atom H on the Pt-M0(111)/C surface1200-- total DOS700]- total Dos1000 t600 1800-500-400-名600300]00-2001200 I100-0_N'Wof-0.5-04-03-02-0.10.00.1 0.2-0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2EHaE/Ha200 ;150.100 :hn _Pt-pp- PIpP1000Q00Ptd-Ptd40040JWM20-00-0--03-02-01000102-o'+ "-o.a" -02 oo" o o证dmMoss.8E.3.012.5 -2.0邕1.011.0 10.0 140]o-0一10-。E/i1Fig. 3. Densty states DOS) of carbon sup中国煤化工(a. Total density states (DOS) of car:HCNMHGb. Total density states (DOS) of carbou ouppuricu r-1u11i;c. Partial density states (PDOS) of atom Pt in carbon supported Pt(111);d. Partial density states (PDOS) of atom Pt in carbon supported Pt-M0(111);e. Partial density states (PDOS) of atom Mo in carbon supported P-M0111))WANG Y. W. et al: Theoretical Study on the Adsorption and1166Decomposition of Methanol over the Pt-M0111)C SurfaceNo. 8product288.6kJmolreactant 。千104. 8kJmolFig. 4. Dissociation pathway for CHzOH on the Pt-M0111)/C surfacePreliminary transition- state geometries are obtainedsmaller tban the total ionic radius of the three atomsusing the integrated linear synchronous transit/qua-(0.294 nm). It indicates that a strong chemical bonddratic synchronous transit (LST/QST) method45); has generated between 0 and Pt -Mo. The distanceand the computational details used are the same as between 0 and its neighboring Pt -Mo reduces tothat of the adsorption process. In dissociation the0.2554 nm smaller than the total ionic radii of theH-O bond is broken, then atoms H and 0 movethree atoms (0.309 nm). The bond lengths of H-Ctowards the surface of crystal substrate, respectively.and 0-C have lttle changes. From Fig. 3, theWe find that atom H tends to the fcc PtzMo site ofproduct is gotten by transition-state. The brokenthe surface, and CH3O moves from the top Pt site toenergy of H-O bond with the Pt -Mo(111)/C catalystthe bridge _Pt site, which are consistent with theis only 104.8 kJ:mor~', indicating that the process ofexperiments46.4n. The distances of H and 0 vary0-H bond breaking is an endothermic reactionfrom 0.0982 to 0.2107 nm in the process ofwhich is favorable to occur over the Pt- Mo(11)/adsorption, and the centric bond making up ofO, HC(111) surface, so carbon supported Pt-Mo alloy isand Pt- Mo has formed and enables the transitionhelpful to the dissociation of methanol.state to exist stably on the suface of substrate. Thatprocess is similar to the adsorption of methane over4 CALCULATION AND DISCUSSIONthe suface of metal, and among atom H, CH3 andFOR NMR OF THE REACTANT ANDmetal the centric bond has formed. Both 0 -Pt- MoUV ADSORPTION SPECTRAand H-Pt -Mo bonds have formed, varying with thebreaking of H-O bond. The energies given out by4.1 NMRthe formation of new bond have supplied theThe NMR calculation was carried out with theenergies needed in the broken process, which indu-Gaussian 98(491program package. The methanolces the activation barrier only to be 288.6 kJ-mor-.molecule gas geometry was optimized with B3LYPMeanwhile, the free methanol molecule wasat the 6-31G (d) level. Then NMR was calculatedoptimized with B3LYP at the 6-31G (d) level, andwith the method GIAO (gauge including atomicthe broken energy of H- 0 bond is 406.4 kJ molr*.orbil中国煤化工) 3 compares theCompared with that of experimental result 430 kJcaleuYHof reactant. Ourmol-148, our calculations are basically consistentcalcuCN M H Gent with expei-with it with the relative error of 5.8%. The distancements with the relative errors among 2.5%, expectof H and Pt-Mo decreases to 0.1954 nm, which is that of H in hydroxyL.2010 Vol. 29结构化学(JIEGOU HUAXUE)Chinese J._ Struct. Chem.1167Table 3. NMR Values ofCHzOHAtomsC)H(2)H(3)H(4)Cbemical shift (cal. values)41.223.490.68Chem. Shift (ref. values"41.63.4,.4,4.1Relative erors0.92%2.5%50.2%4.2 UV absorption spectraenergy is higher than that of the others and reachesWhen exposed to light, the sample molecules haveto 105.0 kJ molr'. Comparing with carbon supportedan energy that matches a possible electronic transi-Pt catalyst, the adsorption capacity of carbontion within the molecule. Some of the light energysupported Pt-Mo alloy is obviously promoted. How-will be absorbed while the electron is promoted to aever, the adsorption energies of the other sites arehigher energy orbital. As a result, the characteristicslower than that of top-Pt site. In the process ofof UV absorption spectra are determined by theadsorption, the geometry of methanol has changed,electronic distribution and conjugation state ofthe lengths of C 0 and 0 H bonds have prolonged,compounds. Different molecules absorb radiation ofbut the C H bond has changed lttle. Simultaneously,different wavelengths. An absorption spectrum willthe ftequency calculation indicates that the vibra-show a number of absorption bands corresponding totional frequencies of C 0 and 0 H bonds are likelystructural groups within the molecule. Since the UVto generate Einstein shift phenomena, especially;absorption band is 8o wide, the wavelength ofO-H bond has been activated. We have noticed thatadsorption peak can stand for band site which isthe form of doping energy-level is mainly ttributedcalled maximum absorption wavelength (max). Weto 4d orbital of the Mo atom. Both sites of valenceused the same method and level as the NMR com-and conduction bands of the doped system shift toputing to study the UV absorption spectra of metha-lower energies, and it is clear that doping elementsnol, and obtained its maximum absorption wave-lead to the enbancement of reaction rate in thelength (Amax = 168.78 nm). For experiment'So, Amx =oxidation step, namely, the catalytic activity has177 nm. The two results are basically coincidentbeen promoted. The transition-state calculation pro-with each other with the relative error of 4.9%.ves that the decomposition of methanol to methoxyand bhydrogen occurs on the Pt-M0(111)/C surface,5 CONCLUSIONwhich is in agreement with the available experimentresults!*s. Comparing with the adsorption energiesThe microcosmic reaction mechanism of the me-of CH3OH on Pt(111)/C surface and that of CO, thethanol adsorption on Pt-M0(111)/C surface has beenadsorption energies of Co is higher, and Pt(111)/Cinvestigated by density functional theory (DFT). Onis favorable to be oxidized and lose activity. 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