J. Phys. Chem. 1991,95, 3727-3730 represented by such a nucleation mechanism for hemispherical centers: eq 3 1 with instantaneous nucleation and edge growth, eq 33 with progressive nucleation and edge growth, and eq 37 with progressive nucleation and growth from the basal area. Therefore, the three nucleation mechanisms have been compared by transformation of the eq 31, 33, and 37 into a linear relationship and fitting the experimental data. The theoretical curves in Figures 3 and 4 were calculated by using these data. Details of this procedure are given in part 11. As can be convincingly seen, the measurements of Figures 3 and 4 coincide excellently with a particular nucleation mechanism, whereas the others deviate considerably. The given examples follow different nucleation mechanisms: (i) Relaxation of octadecanoic acid monolayers at 30 m N m-I and T = 30 OC is described by instantaneous nucleation with hemispherical edge growth. (ii) Relaxation of octadecanoic acid monolayers at 34 mN m-l and T = 20 OC is described by progressive nucleation with hemispherical edge growth. Summing up, this investigation provides clear evidence that the relaxation experiments giving apparent molecular areas as a function of time at constant surface pressure can be explained by a nucleation process for transforming of monolayer material
3727
to 3D centers. The nucleation model presented above is based on homogeneous nucleation and growth of centers with assumed geometrical shape. The theoretical calculation is characterized by two main features: (i) the overall rate of the process is described by convolution of nucleation rate and growth rate and (ii) the overlap of the growing centers is taken into consideration. The theoretical model allows to distinguish between different nucleation mechanisms. Two experimental examples of octadecanoic acid monolayers have been given for different nucleation mechanisms.
Conclusions The nucleation-growth model introduced for apparent area relaxation of insoluble monolayers at constant surface pressure has the potential to quantitatively describe experimental measurements. The derived model possesses general validity for the theoretical description of the transformation of monolayer material to overgrown 3D phase. As a result of the experimental examination, evidence has been given that different nucleation mechanisms occur. Excellent a m d a n c e of calculated and experimental relaxation kinetics has been obtained. Based on this nucleation model, work is in progress to characterize relaxation of insoluble monolayers a t constant surface pressure in more detail. Registry No. Octadecanoic acid, 57-1 1-4.
Removal of Nltrogen Monoxide through a Novel Catalytlc Process. 1. Decomposltlon on Excessively Copper Ion Exchanged ZSM-5 Zeolites Masakazu Iwamoto,* Hidenori Yahiro, Kenji Tanda, Noritaka Mizuno, Yosihiro Mine,t and Sbuichi Kagawat Catalysis Research Center, Hokkaido University, Sapporo 060, Japan (Received: July 23, 1990; In Final Form: October 23, 1990)
Repeated ion exchange of the ZSM-5 zeolite using aqueous copper(I1) acetate solution was found to bring about excess loading of copper ions above an exchange level of 100%. The high activity of the resulting catalyst for NO decompasition was consistent for at least 30 h even at short contact time and low NO pressure. The number of copper ions that can adsorb NO molecules has been determined by a temperature-programmed desorption technique combined with IR measurement; 94% of Cu2+ ions in ZSM-5 were active for the adsorption. The activity of excessively copper ion exchanged ZSM-5 zeolite was slightly reduced by the oxygen in the feed gas while that of the zeolite, of which the loading amount of copper was less than loo%, was greatly diminished under the same condition. SO2completely poisons the activity at 673-923 K, but the activity can be regenerated at the higher temperature treatment.
Introduction Air pollution and acid rain seriously affect the terrestrial and aquatic ecosystems and therefore are very important problems that must be solved as soon as possible.' The exhaust gases from vehicles' engines and industrial boilers contain mainly carbon oxides (CO and C02),nitrogen oxides (NO,), hydrocarbons, sulfur dioxide, particles, and soot. At present, one of the most significant problems is removal of NO,, which is produced during hightemperature combustion. In particular, the decomposition or reduction of nitrogen monoxide (NO) is a dominant target to be achieved because N O is an inert and the major component of NO, in exhaust gases. It is well-known that NO is thermodynamically unstable relative to N 2 and 0 2 at temperature below 1200 K,2 and its catalytic decomposition is the simplest and most desirable method for N O removal. To date, however, no suitable catalyst, of which the activity continues to be high, has been found. This is due to the fact that oxygen contained in the feed or produced in the de-
* To whom all correspondence should be addressed. 'Department of Industrial Chemistry, Faculty of Engineering, Nagasaki University, Nagasaki 852, Japan. 0022-3654191 12095-3727$02.50/0
composition of NO competes with N O for the adsorption sites.2 Thus, high reaction temperature and/or gaseous reductants are required to remove surface oxygen and regenerate the catalytic activity. At present catalytic reduction processes using NH3, CO, or hydrocarbons on V205-Ti02 or Pt-Pd-Rh catalysts have been practically a~plied.',~On the other hand, copper ion exchanged zeolites$-9 Pt/A1203, YBa2Cu30, supported on Mg0,'O Sr2+(1) Crucq, A.; Frennet, A. In Catalysis and Auromoriue Pollurion Control; Elsevier: Amsterdam, 1987; p 1. Bosch, H.; Janssen, F. Catal. Today 1987, 2, 369. (2) Hightower, J. W.; Van Leirsbung, D. A. In The Curalyric Chemistry of Nitrogen Oxides; Klimish. R. L., Larson, J. G.,Eds.; Plenum: London, 1975; p 63.
(3) Harrison, B.;Wyatt, M.;Gough, K. G. In Catalysis;Royal Society of Chemistry: London, 1982; Vol. 5, p 127. (4) Iwamoto, M.;Yokoo, S.;Sakai, K.; Kagawa, S . J. Chem. Soc., Faraday Trans. 1 1981, 77, 1629. (5) Iwamoto, M.;Furukawa, H.; Mine, Y.;Uemura, F.; Mikuriya, S.; Kagawa, S . J . Chem. Soc., Chem. Commun. 1986, 1273. (6) Iwamoto, M.;Furukawa, H.; Kagawa, S . In New Deuelopments in Zeolite Science and Technolop; Murakami, Y., Iijima, A., Ward, J. W., Eds.; Elsevier: Amsterdam, 1986; p 943. (7) Iwamoto, M.;Yahiro, H.; Tanda, K. In Successful Design of Catalysts: Inui, T., Ed.; Elscrvier: Amsterdam, 1988; p 219.
0 1991 American Chemical Society
3728 The Journal of Physical Chemistry, Vol. 95, No. 9, 1991 substituted pero~skite,Il-'~ and Ag
