J . Phys. Chem. 1990, 94, 5896-5900
5896
number of ignited and total sections, respectively heat generation
showing bistability or oscillations, and since heat conduction may be too slow to assure good mixing. Yet, due to experimental difficulties, direct observations of inhomogeneous solutions are still rare. This realization suggests that analysis of observed instabilities should examine the role of inhomogeneity as a source of the observed behavior. The present work suggests that the results protrayed in Figure I can be accounted for by a relatively simple oscillatory model incorporating two dynamics variables; the larger number of variables indicated by the fractal dimension of the trajectory (Figure I ) is unnecessary. Furthermore, one should be careful in employing control of inherently unstable distributed-parameter systems.
M ,N
Acknowledgment. This research was supported by the Fund for the Promotion of Research at the Technion.
9
Notation wire heat capacity CP wire diameter d function defined in eq 1 1 E dynamic functions g h heat-transfer coefficient
Subscripts
9 T' Ta T, T. W
Y a,,
(T
temperature temperature of section i numerated according to phase effective ambient temperature set point temperature attained after ignition variable incorporating control and activity effects shifted temperatures (eq 14) longitudinal coordinate heat generation at T* and their difference (eq 9), respectively
&, /3 Y. 6
x
q,, va
i, j n
slopes of heat generation curve kinetic parameters heat conductivity activity length fraction of section i and of total ignited (+) or extinguished (-) section
of section i, j at the nth time iteration
Superscript time derivative
A Stopped-Flow Electric Dlchroh Study on Adsorption of Metal Chelates by a Colloidal Clay Masahiro Taniguchi, Masami Kaneyoshi, Yuji Nakamura, Akihiko Yamagishi,* and Toschitake Iwamoto Department of Chemistry, College of Arts and Sciences, The University of Tokyo, Komaba, Meguro-ku. Tokyo 153, Japan (Received: February 10, 1989; In Final Form: March 13, 1990)
An apparatus for measuring stopped-flow electric dichroism is constructed. The instrument enables one to measure electric dichroism as a function of time after two solutions are mixed within 6 ms. The adsorption of enantiomeric or racemic
[Ru(phen),12+ (phen = ],lo-phenanthroline) by colloidally dispersed montmorillonite is studied with this instrument. As a result, it is confirmed that the adsorption of racemic [Ru(phen),]*+ occurs by way of two successive paths: first the chelate binds with a clay rapidly within the cation-exchange capacity (CEC) and then it is adsorbed slowly in excess over the CEC.
Introduction Recently we reported that a tris-chelated complex, [ M ( ~ h e n ) ~ ] ~ + (phen = I,lO-phenanthroline), is adsorbed to a clay in different amounts, depending on whether it is added as a pure enantiomer or a racemic mixture.'J Enantiomeric [Fe(phen)s]2+.for example, is adsorbed to the cation-exchange capacity (CEC) of a clay, while racemic [Fe(phen),12+ is adsorbed in 2 times excess of the CEC. The results suggest that racemic chelates are adsorbed as a unit of racemic pair in the interlayer space of a clay. The present paper reports an attempt to study the adsorption reactions of a metal complex by a clay with a stopped-flow electric dichroism apparatus. Stopped flow is a method of mixing two solutions rapidly in order to initiate a reaction within a few milli~econds.~Electric dichroism measures the anisotropy induced in electronic absorption spectrum when a molecule in a solution aligns under a high electric field! In this experiment, a suspension of clay is mixed with a solution of metal chelate. Thereafter, the electric dichroism due to a bound chelate is recorded as a function of time. The amount of adsorbed species as well as its orientation on a clay surface is monitored by the amplitude of the induced dichroism due to a bound species. The change in an electronic absorption spectrum is followed a t the same time to detect any additional processes on adsorption reactions. It is attempted to * T o whom correspondence should be addressed.
obtain kinetic evidence for the racemic adsorption of a metal chelate by a clay. Experimental Section Material. The clay used was sodium montmorillonite purchased from Kunimine Ind. Corp. (Japan).5 About 0.1 g of the clay was dispersed in 100 mL of distilled water under ultrasonic agitation. The cation-exchange capacity (CEC) of the clay suspension was determined by spectroscopic titration with acridine orange as an adsorbate i n d i ~ a t o r . ~Racemic and enantiomeric tris( 1,lophenanthroline)ruthenium(II) chloride ( [Ru(phen),]Clz) were prepared as described previously.6 Instrument. A stopped-flow electric dichroism apparatus was constructed as schematically shown in Figure 1. Two solutions in syringes were pushed under nitrogen gas pressure into a cell. The cell had two gold electrodes with separation of 2 mm and an optical length of 1 .O cm. A linear polarizer was placed in front ( I ) Yamagishi, A.; Soma, M. J . Am. Chem. Soc. 1981, 103, 4640. (2) Yamagishi, A. J . Coord. Chem. 1987, 16, 131. (3) Gibson, Q.H.;Milnes, L. Bioehem. J . 1964, 91, 161. (4) Tricot, M.; Houssier, C. Polyelectrolyres; Technomic Publishing: Westport, CT, 1976; p 43. ( 5 ) Yamagishi, A.; Soma, M. J . Phys. Chem. 1981, 85, 2129. (6) Yamagishi. A. J . Phys. Chem. 1984.88, 5709.
0022-3654/90/2094-5896%02.50/00 1990 American Chemical Society
Adsorption of Metal Chelates by a Colloidal Clay
The Journal of Physical Chemistry, Vol. 94, No. 15, 1990 5897
i 0
5
10
Figure 1. Schematic diagram of an stopped-flow electric dichroism apparatus: ( I ) pistons with syringes; (2) a cell with electrodes; (3) a delay circuit; (4) an electric field pulse generator; ( 5 ) a polarizer; ( 6 ) a photomultiplier; (7) monitoring light.
of the cell to polarize monitoring light for electric dichroism measurements. An electric field pulse (15 kV/cm X 1 ms) was applied at certain delay times ( t d ) after mixing to obtain an electric dichroism signal. An analyzer was added at the back of the cell when electric birefringence was measured. The progress of a reaction was monitored at the same time with the transmittance change in the electronic spectrum. The dead time of mixing of the apparatus was determined by use of the reaction of NiZ+with murexide (MX-). A solution of Ni2S04(8 X IO” M) was mixed with a solution of MX- (1 X lo4 M). The transmittance at 515 nm decreased exponentially with the relaxation time of 5 5 ms. From the observed amplitude of the signal, the dead time of the apparatus was determined to be 6 f 2 ms.
Results 1 . Electric Birefringence of a Clay Suspension after Rapid Mixing. In order to see whether the present apparatus gives correct signals in electrooptical measurements, electric birefringence is measured after mixing a clay suspension (2 X 10-4 g/mL) with water. The light intensity at 600 nm is monitored by setting the polarizations of a polarizer and an analyzer at the angles of 4 5 O and 135O with respect to the electric field, respectively. No metal complex is added to a clay suspension in these experiments. Parts a, b, and c of Figure 2 are the signals taken at 10,40, and 200 ms after mixing, respectively. Since the clay suspension is merely diluted to half of the initial concentration, the identical birefringence signals should be obtained at any t d after mixing. The amplitudes of the signals in Figures 2 are equal within the experimental error, indicating that the apparatus gives constant birefringence amplitudes. On the contrary, the relaxation time for the decay of the induced birefringence is not constant at the various values of td. The relaxation time at td = 10 ms is shorter than the value for a stationary state. It approaches a constant value when the signal is recorded for longer than 40 ms after the solution is mixed. The rate of the decay of the induced birefringence is determined by the rotational relaxation of an aligned particle in the absence of electric field.4 One of the possible reasons for the shorter relaxation time at td less than 40 ms is that the disorientating rate of an aligned clay particle is enhanced by the turbulent motion of a medium remaining after rapid stopping. We therefore conclude that one has to wait at least for 40 ms until the apparatus gives the correct relaxation time after the two solutions are mixed. As mentioned in the Experimental Section, the dead time of the apparatus is 6 ms. Thus it is concluded that the turbulent motion remains much longer than the dead time of mixing. 2. Electronic Spectra of a C l a y / [ R ~ @ h e n ) System. ~ ] ~ + The binding of [ R ~ ( p h e n ) ~ ]by~ +a clay is studied with electronic spectra. Curve a in Figure 3 is the electronic spectrum of optically active [Ru(phen)J2+ in an aqueous solution. When a clay is
0
5 10 t ime\ ms
Figure 2. Electric birefringence signals recorded at td = 10,40,and 200 ms after mixing a clay suspension (1 X IO4 g/mL) with water, respectively.
wavelengt h/nm
Figure 3. Electronic absorption spectra of an aqueous solution of [ARu(phen)J2+ ( 5 X IO4 M) (curve a) and a clay suspension ( 1 X M in CEC) containing the same concentration of the Ru chelate (curve b).
added, the spectrum changes to curve b in the same figure. The absorbance at 265 nm decreases with the concomitant displacement of the band peak a t 450 nm toward a longer wavelength. By plotting the absorbance at 260 nm, AZm,against the ratio of [clay] in terms of CEC to [chelate], AZM) decreases linearly until it is saturated at [clay]/[chelate] = 2 (curve a in Figure 4). Thus enantiomeric [ R ~ ( p h e n ) ~complexes ]~+ are adsorbed by a clay, occupying two cation-exchange sites per molecule. Since the chelate has two positive charges, it is adsorbed within the CEC of a clay. When similar plots are obtained for racemic [Ru(phen)J2+ (curve b in Figure 4), A,,, decreases more steeply until it is saturated at [clay]/[chelate] = 1. Thus racemic [Ru(phen)#+ complexes are adsorbed, occupying one cation-exchange site per molecule. In other words, the racemic chelates are adsorbed in 2 times excess of the CEC. In both of the above cases, the amounts of the adsorbed chelates are correlated with the CEC of the clay. This implies that the adsorption takes place over the whole surface of a clay layer. As will be revealed in electric dichroism measurements, aggregation of clay layers occurs when a clay binds the chelates.
5898
Taniguchi et al.
The Journal of Physical Chemistry, Vol. 94, No. 15, 1990 03r
d
1
0.4
I
I
1.2 I chyi/l
0.0
I
1
1.6 20 chelate)
I
2.4
2.0
I
3.2
Figure 4. Plots of the absorbance at 260 nm,
[email protected] the ratio of [clay] to [Ru chelate]. The Ru chelate is added as an A-enantiomer (curve a) or a racemic mixture (curve b). The initial concentration of [Ru(phen)J*+ = 2 X lod M and [Na2S0,] = 1 X lo-' M.
m
+.
a
I
c.
Lo
b
n
q 4 .Ul
J
I-
I-
L
5
J.
10
(d)
I
1
1
0 0.3 0.6 0.9 time/s Figure 5. A stopped-flow signal at 475 nm when a clay suspension (1 X M) is mixed with a solution of [A-Ru(phen)J2+ ( 5 X IO4 M).
Therefore, it is deduced that, in the final stage of the maximum adsorption, the adsorbed chelates exist both on the external surfaces and in the interlayer spaces of such aggregates. The evidence for the intercalation of the chelates in the interlayer space has been presented from the expansion of the basal s acing of the layers: d(001) was reported to be 17.7 A and 27 for A-[Ruhen)^]^+ montmorillonite and racemic [Ru(phen)J2+ montmorillonite, 3. Stopped-Flow Electric Dichroism Measurements on the Adsorption of [ R ~ @ h e n ) ~by] ~a +Clay. A suspension of a clay (1 X M) is mixed with an aqueous solution of [A-[Ruhen)^]^+ (5 X IOd M). The whole Ru complex is adsorbed by a clay at infinite time. Figure 5 shows the absorbance change at 475 nm after mixing. The increase of the absorbance corresponds to the progress of the adsorption of the complex. Parts a, b, c, and d of Figure 6,show the electric dichroism signals at 4, IO, 100, and 400 ms after mixing the solutions. In these measurements, the monitoring light is polarized parallel with the electric field direction. The increase of the amplitude in the electric dichroism confirms that the amount of the complex bound to a clay increases with time. This is because a free complex gives no electric dichroism since it has too small permanent or induced electric dipole moment to be aligned under electric field. The time courses of the absorbance change at 475 nm, A475, and the electric dichroism amplitude a t 450 nm, AA450, are replotted in Figure 7. It is seen that AdSOincreases until it levels off in about 100 ms, while A47sincreases more slowly so that it still varies in the range of 100-600 ms. From the relative amplitude of the dichroism, A A 4 5 0 / A 4 ~at, infinite time, the reduced linear dichroism, p , for the final state is calculated to be 0.60 according to the equation U 4 5 0 / A 4 S 0 = ( P / w + 3 COS 20) in which 6 is an angle between the electric field and the polarization of the monitoring light4 This value is inserted into the equation p = (-3/8)(1 + 3 COS 2p)@(E)
0
5
10
t im e/m s Figure 6. Electric dichroism signals for the reaction in Figure 5 . The monitoring light is polarized parallel with the electric field. The electric field pulse is applied at td = (a) 4, (b) IO, (c) 100, and (d) 400 ms after mixing.
rp
0
200 t ime/ms
400
Figure 7. Plots of the amplitudes in the stopped-flowsignal (curve a) and in the electric dichroism signal (curve b) against time for the reaction in Figure 5. The amplitudes are both normalized to unity at infinite time. c3
/
/,,,,,@&/,,/ CLAY LAYER
Figure 8. The possible binding structure of [Ru(phen)J2+.
in which is an angle between the threefold symmetry axis of [ R ~ ( p h e n ) ~and ] ~ +the surface of a clay and @ ( E )the orientation function of the clay particle^.^ At @ ( E ) = 0, clay particles orientate randomly in solution. At @ ( E ) = I , all clay particles orient their two-dimensional surfaces in the direction of the electric field.
Adsorption of Metal Chelates by a Colloidal Clay
The Journal of Physical Chemistry, Vol. 94, No. 15, 1990 5899 I
1.01
t
-
0 t ime/ms
I C C
b
time/ms 200
400
I-
0
0
200
Loo
600
time/ms
Figure 9. Plots of the amplitudes in the stopped-flow signal (curve a) and in the electric dichroism signal (curve b) against time. The reactions are a clay suspension ( 5 X IOd M) with (A, top) A-[Ru(phen)J2+ or (B, bottom) racemic [ Ru(phen)J2+. The amplitudes are both normalized to unity at infinite time for the reaction b.
200 400 t ime/ms
Figure 10. Kinetic results for the reactions of a suspension of claychelate adduct with a chelate: (run a) A-[Ru(phen)#+ montmorillonite ( 5 X IOd M) is mixed with A-[Ru(phen)J2+ ( 5 X 10’’ M), and (run b) racemic [Ru(phen),]*+ montmorillonite ( 5 X lod M) is mixed with racemic [ R ~ ( p h e n ) ~ ]( 5~ +X IOd M). The amplitudes in the stoppedflow and electric dichroism signals are shown in part A (top) and part B (bottom) .espectively. (a)
Assuming +.(E) = 1, cp is obtained to be 75’. Thus [ R ~ ( p h e n ) ~ ] ~ + is bound to a clay with its threefold symmetry axis at 7 5 O with respect to the clay surface (Figure 8). The residual increase of A475nm in the time range of 100-600 ms indicates that there exists an additional process after the whole chelate is adsorbed by a clay. One possibility for such a process is that the adduct of a clay and a chelate coagulates to form a larger particle. This is assisted by the fact that the half-life of the decay of the induced dichroism increases from 1.4 to 2.2 ms with the elapse of the reaction time from 100 to 600 ms. Assuming that the clay-chelate adduct takes a shape of a rod with the length L and the radius d, the half-life, r,/Z, is expressed as t,/z =
/
q L 3 / 1 8 k T In (L/d)
in which q, k, and Tare the viscosity of the medium, Boltzmann’s constant, and absolute temperature, re~pectively.~Assuming that L/d = 100, the length of the aggregate is elongated from 0.5 to 0.7 pm from 100 to 600 ms. The absorption spectrum of a bound chelate is presumed to displace toward the longer wavelength as this coagulation process proceeds. It is noted that the layers of clays are parallel with one another in such an aggregate. Otherwise the amplitude of the electric dichroism would not keep a constant value as the size of a clay-chelate adduct increases. We compare the adsorption between optically active and racemic [Ru(phen),12+ complexes. A clay suspension (5 x lod M) is mixed with a 1 X M of either [~i-Ru(phen)~]~+ or racemic [ R ~ ( p h e n ) ~ ] ~Both + . samples contain 5 X lo4 M of NaZSO4. Figure 9a,b shows the time dependences of A475and A450 for the adsorptions of the enantiomeric and racemic chelates, respectively. In both cases, A450 approaches the saturated value more rapidly than A475. The amplitude of A450 a t infinite time is about 2 times larger for the racemic chelate than for the enantiomeric one. Thus the total amount of adsorbed racemic chelates is 2 times larger than that of adsorbed enantiomeric chelates in consistent with the spectrophotomeric titration results (Figure 4). It is noted that initial half of the total change of A4Mfor racemic adsorption is completed within 20 ms after mixing. The rest of the AA450 change takes place gradually in the time range of 100-600 ms. In other words, the adsorption within the CEC of a clay proceeds rapidly, while the further adsorption exceeding (7) Yamaoka, H. Macromolecules 1975, 8, 339
Figure 11. Schemes showing the two paths leading to the racemic adsorption that are studied in Figure 10.
the CEC occurs slowly. Since the kinetic profiles for the initial step are almost the same between the enantiomeric and racemic adsorptions, it is in the latter stage that the racemic pair of the chelates is formed on the surface of a clay. The effect of stereoselectivity on the latter stage in the above experiments is investigated. As experiment a, a clay suspension (1 X M) containing 5 X 10” M of [A-Ru(phen),12+ is mixed As experiment with a solution of 5 X IO” of [Li-R~(phen)~J~+. b, a clay suspension (1 X lo-’ M) containing 5 X 10” M of racemic [Ru(phen)JZ+ is mixed with a solution of 5 X 10” M of racemic [ R ~ ( p h e n ) ~ ] ~Figure +. lOa,b shows the time courses of A475and A A 4 5 0 for these experiments, respectively. It is noted that both A475and AA450 increase more rapidly for (a) than for (b). The initial rate for the increase of A475is 2.7 times faster for (a) than for (b). In run a, the racemic adsorption layer is formed by the binding of the A-enantiomer to a clay on which only its antipodes, A-enantiomers, exist. In run b, A- and A-enantiomers are adsorbed by a clay on which the two enantiomers are distributed probably in a random fashion. Thus, although the same adsorption layer is formed in either run, the final state is attained in a different way in the two runs. Most probably, for run a, the layer is formed merely by the racemic adsorption of the A-enantiomers to unoccupied sites between the A-enantiomers. For run b, however, the process of rearrangement among the adsorbed species is required to achieve the alternative array of the opposite enantiomers. This might be a reason that the rate
5900
J . Phys. Chem. 1990, 94, 5900-5908
of the change of A475is faster for experiment a than for experiment b. These results confirm the stereoselectiveeffect on the adsorption beyond the CEC (Figure 11).
enantiomeric chelate proceeds by way of the rapid binding of the chelate followed by the slow aggregation among the adduct of a clay-chelate. The racemic mixture of the chelate is adsorbed rapidly to the CEC of a clay and then is adsorbed further slowly to the amount of 2 times excess of the CEC. Stereoselectivity is observed when a chelate is adsorbed beyond the CEC when a clay is already adsorbed by either its antipode or the racemic mixture.
Conclusion The mechanisms of the adsorption of enantiomeric and racemic [ R ~ ( p h e n ) ~by ] ~a+colloidally dispersed clay are studied with the stopped-flow electric dichroism apparatus. The adsorption of the
Surface Active Sites of V,O,-SnO,
Catalysts
Fumio Okada, Atsushi Satsuma,* Akio Furuta,+Akira Miyamoto,t Tadashi Hattori, and Yuichi Murakami Department of Synthetic Chemistry, Faculty of Engineering, Nagoya University, Furo-cho, Chikusa- ku, Nagoya 464, Japan (Received: March 30, 1989; In Final Form: March 14, 1990)
The surface active sites on V205-Sn02catalysts, Le., redox sites and acid sites, were investigated by using two series of catalysts prepared from different starting materials: Sn(OH)2and SnO. By use of the NO-NH3 rectangular pulse technique, it was found that the surface concentration of the redox sites increases with the addition of Sn02,depending strongly on the starting materials at lower Sn02 content. Based on XRD, IR,ESR,XPS,and SIMS data, the increase in the redox sites is attributed to the reduction of vanadium oxide caused by atomic mixing of vanadium and tin oxides. The difference between the two series of catalysts is attributed to the degree of mixing, which may result from the difference in chemical processes during the calcination of precursor of the catalysts. The strengths, surface concentrations, and types of acid sites were determined by using NH3 TPD and IR of adsorbed NH, and pyridine. The properties of the acid sites on the VZO5-SnO2catalysts appear to be due just to those of pure V2OS and Sn0,. Finally, the effects of various promoters, Le., P205,WO,,MOO,, and Sn02,on the redox sites are summarized, and two important factors responsible for the increase in the concentration of the redox sites are discussed: (1) the mixing of vanadium and promoter ions at the surface rather than the formation of intermediate compounds or solid solution in the bulk and (2) a redox function of the promoter oxides.
introduction Sn02 is often used as a promoter of or a support for V Z 0 5 catalysts for the oxidation of naphthalene,' benzene,2 and various organic compound^.^ Although a number of patents have been reported, there are only a few investigations of the promoting effects of Sn02. In most studies,&' the catalytic properties of V,O5-SnO2 have been related to the crystallographic phase. Andersson4 and Madhok5 suggested that lower valent vanadium oxides are stabilized by the addition of SnO, to V 2 0 5and that the boundary between V205and V6013is active and selective for oxidation reactions. Ono et aL6 suggested that the addition of S n 0 2 to V205results in an amorphous phase from which lattice oxygen is easily released. At higher SnO, content, it is expected that a solid solution of Snl-, V,02 ( x < 0.2) plays an important role in catalyzing the oxidation r e a ~ t i o n . ~ The activity and the selectivity of the catalysts directly depend on the surface active sites, i.e., redox sites and acid sites. As for the acid sites, Ai8 suggested that the activity and selectivity can be fairly well explained by the acid-base properties of the V205-SnOZ catalysts and reactants. In the oxidation reactions, however, it is natural to consider that the redox sites are more important in determining the catalyst performance. Although the surface redox sites of V2O5, i.e., the surface V=O species, have been well investigated for the selective oxidation of hydrocarbonsQand the reduction of NO with NH3,I0the effects of SnO, on the surface V = O species have never been reported. Thus, the purpose of this paper is to determine the number and properties of the surface active sites of V205-Sn02 catalysts, i.e., the redox sites and the acid sites. Kinu-ura Research Department, JGC Corporation, Sunosaki-cho, Handa, Aichi 475, Japan. *Present address: Department of Hydrocarbon Chemistry, Faculty of Engineering, Kyoto University, Sakyo-ku, Kyoto 606, Japan.
0022-3654/90/2094-5900$02.50/0
Since the activity and selectivity often vary with preparation method or starting materials used, the type of the number of the (1) Dutch 64,824, 1949; Japan 6274, 1953; Japan 3884, 1955; Brit. 882,089, 1959; Ger. 1,135,883, 1962; Japan 3884, 1962; Japan 34,138, 1973; Japan 41,273, 1974. (2) Solomin, A. V. Izo. Akad. Nauk Kaz. SSR, Ser. Khim. 1957,1,58. (3) (a) Komatsu, F.; Ozono, Y.; Sakurai, K.; Komori, H. Koru Taru 1960, 12,420. Umarova, R. U.;Sembaev, D. Kh.; Suvorov, B. V. Izu. Akad. Nauk Kaz. SSR, Ser. Khim. 1969, 19, 30. (b) Neth. Appl. 6,413,133, 1965; Fr. 1,535,813, 1969; Ger. 2,354,425, 1975. (4) Andersson, A. J . Caral. 1981, 69, 465. (5) Madhok, K. L.React. Kiner. Caral. Len. 1984, 25, 159. (6) Ono,T.; Nakagawa, Y.; Kubokawa, Y. Bull. Chem. SOC.Jpn. 1981, 54, 343. (7) Vickerman, J. C. In Catalysrs; Kemball, C., Dowden, D. A,, Eds.; The Chemical Society, Burlington House: London, 1978; Vol. 2, p 135. Pomonis, P.; Vickerman. J. C. J. Carol. 1984, 90, 305. (8) Ai, M. J . Caral. 1975, 40, 318. (9) (a) Cole, D. J.; Cullis, C. F.; Hucknall, D. J. J. Chem. SOC.,Faraday Trans. 1 1976, 72, 2185. (b) Akimoto, M.; Usami, M.; Echigoya, E. Bull. Chem. Soc. Jpn. 1978,51,2195. (c) Bond, G. C.; Stirkany, A. J.; Parfitt, G. D. J. Caral. 1979,57,476. Bond, G. C.; Konig, P. Ibid. 1982, 77, 309. (d) Anpo, M.; Tanahashi, I.; Kubokawa, Y. J. Phys. Chem. 1980,84, 3440. (e) Andersson, A.; Lundin, S.T. J. Caral. 1979, 58, 383; 1980, 65, 9. Jonson, B.; Rcbenstorf, B.; Larsson, R.;Andersson, S.L. T.; Lundin, S.T. J. Chem. Soc., Faraday Trans. 1 1986,82,767. ( f ) Mori, K.;Inomata, M.; Miyamoto, A.; Murakami, Y. J . Phys. Chem. 1983,87,4560; J . Chem. Soc., Faraday Trans. 1 1984, 80, 2655. Mori, K.; Miyamoto, A.; Murakami, Y. J. Phys. Chem. 1984,88,2735,2741,5232; 1985,89,4265. (8) Tanaka, T.; Ooe, M.; Funabiki, T.; Yoshida, S. J . Chem. SOC.,Faraday Trans 1 1986, 82, 35. Tanaka, T.; Tsuchitani, R.; Ooe, M.; Funabiki, T.; Yoshida, S.J. Phys. Chem. 1986, 90,4905. (h) Hengstun, A. J.; hanger, J.; Hengstum-Nijhuis, S.M.; Ommen, J. G.; Gellings, P. J. J . Catal. 1986, 101, 323. (10) (a) Inomata, M.; Miyamoto, A.; Murakami, Y. J. Caral. 1980,62, 140. Miyamoto, A.; Inomata,M.;Hattori, A.; Ui, T.; Murakami, Y. J . Mol. Caral. 1982,16,3 15. Miyamoto, A.; Kobayashi, K.; Inomata, M.; Murakami, Y. J. Phys. Chem. 1982, 86, 2945. Miyamoto, A,: Yamazaki, Y.; Hattori, T.; Inomata, M.; Murakami, Y. J . Catal. 1982, 74, 144. (c) Bosch, H.;
Janssen, F. J. J. G.; Kerkhof, F. M. G.; Oldenziel, J.; Ommen, J. G.; Ross, J. R. H. Appl. Caral. 1986, 25, 239.
0 1990 American Chemical Society
