Title. Author(s)TANAKA, Ken-ichi. Issue Date Doc URL. Type. File Information INTERMEDIATE OF HOMOMOLECULAR OXYGEN EXCHANGE REACTI TEMPERATURE

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1 Title NTERMEDATE OF HOMOMOLECULAR OXYGEN EXCHANGE REACT TEMPERATURE Authr(s)TANAKA, Ken-ichi CitatinJOURNAL OF THE RESEARCH NSTTUTE FOR CATALYSS HOKK ssue Date Dc URL Type bulletin File nfrmatin 23(3)_P pdf nstructins fr use Hkkaid University Cllectin f Schlarly and Aca

2 J. Res. st. Catalysis, Hkkaid Univ., Vl. 23, N.3, pp. 171 t 175 (1975) NTERMEDATE OF HOMOMOLECULAR OXYGEN EXCHANGE REACTON AT LQUD NTROGEN TEMPERATURE By Ken-ichi TANAKA *J (Received Nvember 18, 1975) Abstract The hmmlecular xygen exchange reactin reactin takes place far mre rapidly at liquid nitrgen temperature than at rm temperature ver ZnO and n Ti 2 The super xide ins adsrbed n these xides d nt take part in this lw temperature exchange reactin. n this paper, a neutral 4 intermediate is infered fr this lw temperature exchange reactin instead f the 4" having been prpsed in the referrnces. n these several years, the three frms f adsrbed xygen species, -, O2 and 3, have been firmly established by using ESR technique!!, and nw ur interesting is fcussing n the reactivity and/r the selectivity f these species in the catalytic xidatin reactins. The authr has shwn that - is the reactive intermediate f the catalytic xidatin f CO n ZnO in dark and under illuninatin 2,3) and O2 n the ZnO r TiO z is less reactive fr the xidatin reactins as well as fr the istpic exchange reactins with CO and O 2 4 ) NACCACHE 5 ) has als shwn the high reactivity f - n MgO fr O 2, CO and C 2 H 4 The authr9) has fund that a small amunt f CO inhibites strngly the hmmlecular xygen exchage reactin n ZnO under illuminatin, which make us t prpse 3 intermediate fr the exchange reactin under illuminatin,b,9) that is, the higher reactivity f - with CO than that with O 2 disturbes the frmatin f 3. This paper gives the evidences shwing ther intermediate fr the hmmlecular xygen exchange reactin taking place at liquid nitrgen temperature in dark. Experimental ZnO f.43 g (Kadx-25 frm New Jersey Zinc C.) and rutile type Ti 2 f.55 g (Titanx RA-lO frm Titanium Pigment C.) were used as *) Research nstitute fr Catalysis, Hkkaid University, Sappr, Japan. 171

3 172 K. TANAKA catalyst. These xides were treated with xygen at 41O...,42 C fr several hurs and were evacuated fr mre than 12 hurs at the same temperature. After the evacuatin, the catalyst was cled in vacuum and was subjected t the experiments. The istpic analysis f gas phase xygen as well as the desrbed xygen were carried ut by cnnecting the reactr directly t the mass spectrmeter. Oxygen-8 (ca. 9 atm %) frm YEDA R&D C. and Oxygen-6 frm Takachih Kagaku Kgy were used withut further purificatin. Results and Discussin A mixture f 16 2 and 18 2 f.6 trr was admitted t the zinc xide at rm temperature. Hmmlecular exchange reactin ver zinc xide at rm temperature was t slw t measure the reactin, and few exchange reactin tk place even after 8.5 hurs. The rate f the equilibratin, hwever, substantially increased at liquid nitrgen temperature, and the gas phase cmpsitin arrived t abut 74% f the equilibratin within 3 minutes as shwn in Figure 1. After the evacuatin f the gas phase xygen at liquid nitrgen temperature, the ~ Gas phase Physisrptin c r-l 16 f) 2 a. E u u.. - f)... 5 r- 6'8 i '~ i! : Time (min.) Fig. 1. The istpic equilibratin, ~ , n ZnO at liquid nitrgen temperature. Dtted lines are the calculated equilibrium cmpsitins.

4 173 ntermediate f Hmmlecular Oxygen Exchange Reactin at Liquid Nitrgen Temperature reactr was warmed t rm temperature t make the analysis f the weakly adsrbed xygen. The istpic cmpsitin f the desrbed xygen between liquid nitrgen temperature and rm temperature is shwn in Figure 1 as the physisrbed xygen. t is bvius that the xygen desrbed between liquid nitrgen temperature and rm temperature is mre clse t the equilibrium cmpsitin than the gas phase xygen having been evacuated at liquid nitrgen temperature. Where the time f 35 minutes n abscissa indicates that abut 5 minutes was required t warm up the reactr frm liquid nitrgen temperature t rm temperature. n the previus paper, it has been shwn that the xygen adsrbed n the evacuated ZnO r n Ti 2 gives a desrptin spectrum having a maximum at arund 18 C, which has been assigned as super xide in, O2, by ESR. n rder t thrw light n the participatin f the O2 upn the istpic exchange reactin at liquid nitrgen temperature, the istpe analysis f the desrbed xygen was made by rising the reactr's temperature, and was cmpared with the istpic cmpsitin f the gas phase xygen in the fllwing experiments. Abut 1 trr f 18 2 was admitted t the zinc xide n which 16 2 had been previusly prepared at rm temperature by 1~ ' Ga~hase ~sisrpr-t_i_n C_h_e_m_is r.:...p_ti_n_--'1 c E 5 f : : :! : : : : 162 : :: l:1 : :1: : l ' 1 OL-~~L4 ~.. ~LD' ~~!LD ~~!lld ~~llb ~:~ ~ Lliq N2~ "-' 12 '"V 155 "'-'19 Time (min) Thermal Desrptin (OC) Fig. 2. stpic mixing between adsrbed 16 2" and gas phas 18 2 at liqid nitrgen temperature, and the istpic distributin in the desrbed xygen [2"]. Dtted lines are the calculated equilibrium cmpsitins.

5 174 K. TANAKA cntacting with Abut ne minutes later, the reactr was cled t liquid nitrgen temperature and kept it at that temperature fr 6 minutes, which is sufficient time t detect the istpic exchange at liquid nitrgen temperature if ccurs as is knwn frm Figure 1. The istpic cmpsitin f the gas phase xygen as well as that f the physisrbed xygen were shwn in Figure 2. After the analysis f the physisrbed xygen, the zinc xide was evacuated fr 3 minutes at rm temperature and was fllwed t the thermal desrptin experiment by rising the temperature. As shwn in Figure 2, desrbed xygen cntains 18 2 and The fractin f xygen-18 in the desrbed xygen decreases as increasing the desrptin temperatures, and the istpic distributin is unambiguusly far frm the equilibrium distributin. The mixing f xygen-18 bserved n the desrbed xygen can be well explained by a simple replacement f the adsrbed 16 ; with 18 2 and in gas phase accmpanying n istpic scramble; 182(y) + 16 ; (a) ~ 18 ; (a) + 162(y) 18Q 16 (y)+ 16 ; (a) ~ 1816-(a)+ 162(y). n rder t make clear the replacement f the adsrbed xygen with gas phase ne, 18 2 f abut 1 trr, having the value f 1816/( ) ~ c,q +- (/) a. 5 () 'a' +- (/)... Fig Temp (OC) Replacement f adsrbed xygen with 18 2 n ZnO at rm tempeature. -Q-, '. and"" are derived frm Figure 2, 3

6 175 intermediate f Hmmlecular Oxygen Exchange Reactin at Liquid Nitrgen Temperature =.182, was cntacted with the 16 2 preadsrbed ZnO at rm temperature fr 5 minutes, and was evacuated fr 2 minutes at rm temperature. The istpic cmpsitin f the desrbed xygen is shwn in Figure 3, in which the values f 1816N ) are apprximately equal t the valus f the 18 2 used. This result undubtedly indicates that the xygen-18 mixing in the desrbed xygen is mainly caused by the simple replacement between the adsrbed xygen and the gas phase xygen. The istpic cmpsitin btained in Figure 2 at the varius desrptin temperatures is fund t give the equal distributin shwn in Figure 3 as indicated with the symbls with hk. n the previus wrks n the phtcatalytic exchange reactin n ZnO and n Ti 2,8,9l 3 species have been prpsed as an intermediate f the phtcatalytic exchange reactin f xygen. The phtcatalytic exchange reactin has been fund t be strngly prhibited by a small amunt f carbn mnxide, which has been explained by the prmpt reactin f CO with - species prhibiting the frmatin f 3, the intermediate f the exchange reactin. n cntrast with the phtcatalytic exchange reactin f xygen, the exchange reactin taking place at liquid nitrgen temperature takes few influence by CO additin. These results btained in the present experiments, accrdingly, reveals the new type intermediate fr the lw temperature istpic mixing f xygen. n cnfrmity with the fact that the super xide ins, O2, d nt exchange with gas phase xygen at liquid nitrgen temperature, the 4 frmed frm O2 and O 2 shuld be ruled ut, and a neutral 4 species may be prpsed as a plausible intermediate f this lw temperature exchange reactin. This result will be cnfirmed by using xygen-17 and ESR technique. References 1) J. H. LUNSFORD, Catalysis Rev., 8, 135 (1973). 2) K. TANAKA and G. BLYHOLDER, Chern. Crnrn., 736 (1971). K. TANAKA and G. BLYHOLDER, J. Phys. Chern., 76, 187 (1972). 3) K. TANAKA and G. BLYHOLDER, Chern. Crnrn., 1343 (1971). 4) K. TANAKA and K. MYAHARA, Chern. Crnrn., 877 (1973). 5) C. NACCACHE, Chern. phys. Lett., 11, 1323 (1971). 6) T.. BARRY and F. S. STONE, Prc. Ry. Sc. (Lndn), A 335, 124 (196). 7) K. HROTA and M. CHONO, J. Catalysis, 3, 196 (1964). 8) K. TANAKA, J. phys. Chern., 78, 555 (1974). 9) K. TANAKA and K. MYAHARA, J. phys. Chern., 78, 233 (1974).