SiO2

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...

...,..I...............

. . . .. . . . . . . . . . . . .. . .

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,$i$::::. .. Applied Surface North-Holland

Science

68 (1993) 257-264

applied surface science

The influence of calcination temperature and hydrogen solubility in Pd/SiO, Jorge H. Septilveda

and Nora S. Figoli *

INCAPE, Institute de Investigaciones en Cat&is 3000 Santa Fe, Argentina Received

2 November

on Pd dispersion

1992; accepted

y Petroquimica (FIQ, UNL - CONICET),

for publication

14 January

Santiago de1Ester0 2654,

1993

The relation between Pd particle size and hydrogen solubility in Pd/SiO, was quantitatively studied by means of several techniques such as TPR, hydrogen TPD, TRS, TEM and H, chemisorption. When correlating solubility, defined as HJPd,, with dispersion, two zones were observed: one for high dispersion values having a H,,/Pd, ratio of 0.36 and the other having higher values, for lower dispersions. The hydrogen solubility in bulk Pd (H,/Pd,) has a constant value of 0.7 for dispersions up to 80%; for very small metal particles this value increases up to 6.

1. Introduction

Palladium is one of the most useful Group VIII metals for hydrogenation reactions [1,2]. The metal particle size in metal supported catalysts is very important due to the existence of structuresensitive reactions [3,4]. For this reason it is important to control the metal particle size during catalyst preparation. It is well known that small particles can be obtained by ionic exchange followed by the use of adequate thermal treatments. Hydrogen is both adsorbed on and absorbed in Pd. The absorbed Pd has been correlated with catalytic activity [5,61 and consequently, the quantification of absorbed hydrogen is very important. Hydrogen absorption in bulk palladium black has been extensively investigated but there is a lack of studies on very small palladium crystallites. Aben [7] found that the total amount of hydrogen uptake in the P-phase decreases as the dispersion of palladium increases, and he attributes this observation to the decrease of hydrogen solubility with increasing dispersion of the metal. However, Boudart and Hwang 181considered that the effect

* To whom correspondence 0169-4332/93/$06.00

should

be addressed.

0 1993 - Elsevier

Science

Publishers

of palladium dispersion on hydrogen solubility requires a subtle distinction between surface and possible kinds of subsurface hydrogen atoms. The aim of this paper is to study the influence of thermal treatments on the dispersion of Pd/SiO, catalysts prepared by ionic exchange and the relation between hydrogen solubility and metal particle size. Two types of H, solubility are defined: (9 H,/Pd,, (ii) H,/Pd,, where H, = absorbed hydrogen, Pd, = total palladium, Pd, = surface palladium, Pd, = bulk palladium = Pd, - Pd,.

2. Experiment 2.1. Catalyst preparation Catalysts were prepared by ionic exchange starting from Pd(NO,), or PdCl,, which were dissolved in NH,OH at pH = 11. SiOZ Grace G-57 (S, = 270 m* g- ‘) was kept in NH,OH solution, before and during the addition of the basic Pd solution. A liquid/solid ratio = 25 was

B.V. All rights

reserved

258

J. H. Sepilveda, N.S. Figoli / Pd dispersion and hydrogen solubility in Pd / SiO,

used. The Pd concentration in the solution was measured as a function of the time of exchange by atomic absorption spectrometry (Perkin-Elmer Model 5000). The solids, after being dried at 110°C were calcined in air at different temperatures, under 20 ml min -’ flow rate during 120 min and then reduced at 300°C (Catalysts CR). Another catalyst was prepared by impregnation, starting from Pd(NO,),; it was calcined and then reduced at 300°C. The Pd content of the catalysts (Pd,) was measured by chemical analysis. 2.2. Temperature-programmed reduction and temperature-resolved sorption (TRS)

(TPR)

TPR was performed in a flow apparatus under the following conditions: 5% H, in Ar; gas flow rate, 10 ml min -‘; linear heating rate (p>, 6°C min -’ from -80 to 400°C. Temperature was kept at 400°C for 30 min and the sample was then cooled down to room temperature, for performing the TRS. The H, desorption and consumption was followed by a thermal conductivity detector (TCD). 2.3. H2 chemisorption It was performed by the hydrogen back-sorption method [91, using a volumetric adsorption system at room temperature, with the following steps: (a> outgassing at 300°C during 30 min; (b) reduction at 3OO”C,during 60 min; (c) outgassing at 300°C during 60 min; (d) H, uptake at room temperature; (e) outgassing at room temperature, during 30 min; (f) H, uptake at room temperature; (g) outgassing at room temperature; (h) dead volume determination. The first H, uptake (step d) corresponds to both adsorbed and absorbed hydrogen. During outgassing at room temperature, only absorbed hydrogen is eliminated [8]. During step f the hydrogen uptake corresponds to absorbed hydrogen.

2.4. H, temperature-programmed

desorption (TPD)

Parameters and experimental conditions were chosen in order to eliminate intraparticle mass transfer resistance and re-adsorption. Experiments were performed following steps a-f: (a) reduction at 300°C during 120 min; (b) treatment with Ar (50 ml min-‘1 at 400°C during 60 min; (cl cooling to room temperature under Ar stream (30 ml min- ‘>; (d) H, uptake (30 ml min- ‘) at 0°C during 20 min; (e) treatment with Ar (50 ml min-‘1 at 0°C during 20 min; (f) linear heating (15°C min-‘1 under Ar (30 ml min-‘I. 2.5. Differential thermal analysis (DT) Air at 50 ml mini’ was used with a heating rate t/3) = 20°C min-’ in a Shimadzu DT-30 equipment. 2.6. Transmission electron microscopy (TEM) Catalysts were examined in a JEOL 100 CXII electron microscope in order to determine Pd particle size. Samples were ultrasonically dispersed in bidistilled water, and the suspension was collected on copper grids, containing Formwar film. Determinations were carried out at 100 kV with a 20 pm condenser aperture. The specimen exhibited a great stability under the beam. Pretreatment of the grid at 150°C in vacuum prior to the sample introduction, greatly reduced the contamination level of samples. Spherical particles were assumed for calculations.

3. Results 3.1. Catalyst preparation

During Pd cationic exchange [lo], the species present in the solution at pH = 11 is [Pd(NHJ412+, as it has been mentioned in several references [11,13].

259

J.H. Septilveda, N.S. Figoli / Pd dispersion and hydrogen solubility in Pd / SiO, Table 1 Modification as a function

of the Pd concentration of time

in the exchange

Time (min)

Pd (mg/l)

Pd (mg/l)

Initial 2.5 30 60 180 300 900 1200

140.8 6.3 4.0 3.0 1.5 1.2 0.8 0.8

148.0 7.7 5.0 3.2 2.9 2.4 2.1 2.0

solution

Table 1 shows, for the two precursor salts used, the exchange of Pd as a function of time. Pd was almost completely exchanged after 15 min for both PdCI, and Pd(NO,),. The percentage exchange after that time was nearly 95%. The final Pd content on the catalysts was 0.3% in both cases, as measured by chemical analysis. 3.2. Temperature-programmed perature-resolved sorption 3.2.1. Temperature-programmed

0

320

160

Temperature

480

( “C 1

Fig. 1. Hydrogen TPR profiles for catalysts Pd/SiO, from Cl-: (a) calcined at 100°C; (b) calcined at 200°C; (c) calcined at 300°C; (d) calcined at 400°C; (e) calcined at 500°C; (f) calcined at 600°C.

reduction and tem-

reduction

Reduction profiles indicate that the peak maxima are clearly related to the calcination temperature (CT), as it is clearly shown in fig. 1 and table 2 for catalysts obtained from PdCl,. When CT is lower than 200°C the reduction profile is broad and its maximum is above 200°C; when CT is higher than 3OO”C, the maximum occurs at lower temperatures and slightly decreases with increasing CT. The peak is sharper, as well. 3.2.2. Temperature-resolved sorption When cooling the catalyst after the TPR experiments, it is known [6] that H, is again chemisorbed and that it is also absorbed in the bulk of Pd. The peak appearing at approximately 250°C corresponds to adsorbed hydrogen (H,,) and the one appearing at around 90°C corresponds to absorbed hydrogen (H,) [6]. Fig. 2 shows the TRS spectra of one of the catalysts, Integrating the adsorption and absorption peak areas and considering the stoichiometry H,,/Pd,

Table 2 Temperature (T,) occurs,

at which the maximum of the reduction as a function of the calcination temperature

Catalysts

Calc. temp. CC)

T,,, (“0

CR100 CR200 CR300 CR400 CR500

100 200 300 400 500

240 210 123 108 107

7

=! 0

Temperature Fig. 2. TRS profile of catalyst

(‘Cl CR100.

peak

J. H. Sephlueda, N.S. Figoli / Pd dispersion and hydrogen solubility in Pd / SiO,

260 Table 3 Dispersion sorption

and

3.3. H, chemisorption

H, /Had

values

from

temperature-resolved

Catalysts

Calc. temp. (“C)

Dispersion (%I

H,/H,,

H,/H,,

CR100 CR200 CR300 CR400 CR500 CR600

100 200 300 400 500 600

43 70 77 76 79 21

0.47 0.34 0.17 0.16 0.18 1.40

0.56 0.37 0.35 0.33 0.34 4.09

hydrogen

chemisorption

a) From

The results of H, adsorption and those of absorption for catalysts with different thermal treatments are presented in table 4. When changing the CT from 100 to 600°C a wide range of dispersions is obtained because partial or total de-ammination occurs during calcination, producing several Pd species with different mobilities, resulting in either small or large metal particles [16]. The mean metal particle size for one of the samples obtained using this method, was compared to the result from TEM, with a good agreement. The differences in the dispersion values with those shown in table 3 can be attributed to the considerations made about the validity of eq. (1).

a)

(table 4).

= 1 (Had = adsorbed hydrogen), it is possible to calculate the dispersion [14,15] according to: D(%)

=

Pd,[H,, Pd,[H,,

area]

area + 2.77H, area] .

(1)

3.4. Thermal-programmed

The 2.77 value is due to the assumption that the hydride is formed with the following stoichiometry: Pd, + O.l8H, + PdH0.36.

Fig. 3 shows the H, desorption profile for the catalyst CR300 (d= 12.2 A). Experiments were carried out under experimental conditions so as to avoid intraparticle mass transfer resistance, which according to Rieck and Bell [17] is negligible for particles between 30 and 60 mesh. The four dimensionless numbers described by Gorte [18] were considered avoiding the lag time for sample measurement and the accumulation of gas in the catalyst pores. Concentration gradients as well as re-adsorption are difficult to avoid and

(2)

Nevertheless, calculations using eq. (1) are approximate. The absorption peak is around 90°C while in eq. (2) the stoichiometry is assumed at room temperature.As it will be demonstrated later, stoichiometry is only true for certain particle sizes. Results are presented in table 3 where the ratios between the areas of absorbed (H,) and adsorbed (Had) hydrogen are also shown.

Table 4 Hydrogen treatments Catalyst

chemisorption,

mean

particle

Thermal treatment

CR100 CR200 CR300 CR400 CR500 CR600

Calc. Calc. Calc. Calc. Calc. Calc.

100 200 300 400 500 600

‘) ‘) ‘) ‘) ‘) ‘)

a) Assuming spherical particles, b, From TEM. ‘) & reduced at 300°C.

6=

size and

dispersion

desorption

values

of Pd/SiO,

(from

PdCl,)

catalysts

with different

H 2 (ads)

H, cabs)

D

(j a)

2 b)

(pm01 g-l)

(pm01 g-‘)

(%)

(A,

(A,

7.4 12.0 13.5 12.7 12.5 2.1

4.2 4.5 4.8 4.3 4.3 8.6

53 85 95 90 89 15

21.8 13.6 12.2 12.9 13.0 77.0

19.0

11.57/O.

thermal

J.H. Sepilveda, N.S. Figoli / Pd dispersion and hydrogen solubility in Pd / SiO,

may increase the peak temperature considerably. This did not happen in our experiments because the two principal peaks (desorption of absorbed H, at 25°C [19] and desorption of adsorbed H, at 90°C [20-221 appear at low temperatures. The third peak appearing at a higher temperature is broad and, according to Lear-y et al. [23] and Conrad et al. [24], corresponds to the desorption of adsorbed hydrogen that diffuses in the bulk after desorption is depleted. The adsorbed hydrogen desorption energy (E,) was calculated assuming second order with freely occurring re-adsorption using the following equation [25,26]: 2 log T, - log p = E,/2.3RT,,, + log[ (1 - 0)3V,VmE,/(20,FA*R)],

(3)

where em is the coverage at T = T,; T, (K) is the temperature at the maximum; /3 (“C min-‘) is the heating rate; V, (ml) is the bed volume; V, (pm01 ml-‘) is the amount of gas adsorbed for total coverage per unit volume of the metal phase; F (mol s-l) is the carrier flow rate: R is the gas constant; A* = exp(S/R) where S is the entropy of desorption.

Table 5 Experimental

parameters

p = 0.16”C s-’ F, = 0.5 ml s-‘:

261

used in H, TPD studies

F = F,,(T/

T,,)

Jp (catalyst mean particle diameter) = 0.0298 cm D = 85%, V, = 8.8 exp - 6 mol cm-’ V, = 0.18 cm3 (bed volume) 0 = 0.36; l ,Z$= 28 (Cvetanovic and Amenomiya [38]) A* = exp(SHZ /R)

To calculate E,, it is necessary to know the position of the maximum of the desorption peak corresponding to adsorbed H,; the other quantities are easily measurable. The experimental parameters used in our experiments are presented in table 5. The E, value found for the different catalyst was 79 kJ/mol. Other authors have found slightly higher values; Konvalinka and Scholten [191 found an E, value of 90 + 5 kJ/mol for Pd/C, similar to that found by Conrad et al. [24]; Rieck and Bell [22] observed two peaks for the desorption of adsorbed hydrogen on Pd/SiO, which were assigned to the (111) and (100) planes and having E, = 88 and 102 kJ/mol, respectively. The latter two authors postulated that the adsorption strength decreases for more dispersed particles. 3.5. Differential thermal analysis

5o r

The solids dried at 40°C are white due to the presence of [Pd(NH,),l’+ species [16,27]; after calcination at 110°C they are yellow due to the

0

I’ 0

t loo

1

200

I

300

Temperature Fig. 3. Hydrogen

1

400

I

I

500

600

(“C)

TPD profile of catalyst

CR300.

I

I

I

I

100

200

300

400

Temperature

500

( “C1

Fig. 4. DTA profile of catalyst Pd/SiO, from Cl-: at 40°C; (B) dried at 110°C.

(A) dried

J.H. Seplilveda, N.S. Figoli / Pd dispersion and hydrogen solubility in Pd / SO,

262

presence of [Pd(NH,),]*+ species [16,27]. After calcination at 500°C the solids are orange-brown. Other colour changes occur between 100 and 500”. The DTA profile of the sample dried at 40°C presents two peaks (fig. 4). The first, endothermic, is broad and its minimum occurs at 85°C; the second is exothermic and sharp and its maximum occurs at 245°C. When the solid has been dried at 110°C the first peak maximum is shifted to 78°C and the peak is not so broad.

maximum at 245°C and finishes at about 300°C and can be assigned to the ammine ligands. TPR profiles of samples calcinated at 100 and 200°C show peaks that are wide and asymmetric, indicating a non-uniform reduction process [28] that is related to the ammine ligands still attached to Pd. For samples calcined at higher temperatures, the peaks are sharp, almost independent from the CT and very similar to those obtained from a catalyst prepared by impregnation. According to the experimental results (DTA and TPR) it can be assumed that the reaction:

4. Discussion

[Pd(NH;)4]2++

4.1. The effect of thermal treatments on dispersion

occurs below 110°C. The [Pd(NH,),l*’ complex is decomposed at about 300°C through reactions (5) or (6):

The reduction profiles of the catalysts prepared by ionic exchange are related to calcination temperature (CT) due to the different Pd species that are formed from [Pd(NH,),12’, as it was also found on Pd/zeolite [16]. Since the reduction profiles do not show important changes for CT above 300°C it is possible that all the ammine ligands have been eliminated when a CT of 300°C is reached. For an acid system (Pd/NaY), for which it is more difficult to eliminate the ammine ligands totally, Homeyer and Sachtler [16] have found that only 18% of the ammine ligands are retained after calcination at 300°C. The second peak in the DTA profile (fig. 4) presents the 0.8

\ 5 5

0.6

clx NO; . Impregnation

0

\

Y

l\

\ ‘1

z \, 0.4

\

\

.

‘QL-X_ .

I

-b-x’R,-

0.2

0

I

u

20

1

40 Dispersion

60

80

2 NH,

(4)

+ ; 0, + Pd*++ N, + 3 H,O (5)

[Pd(NH,),]*++

Pd2++ 2 NH,

(6)

For these catalysts, changes in the dispersion for calcination temperatures higher than 300°C should not be expected, as the only species present is Pd*+, free of ammine ligands; the decrease in dispersion for CR600 is due to sintering, as it can be expected for catalysts heated at temperatures above 500°C [29]. Consequently, the size of the metal particle after reduction in the CR series depends on the species formed during calcination. Homeyer and Sachtler [16] have found that higher dispersions can be obtained maximizing the diammine/tetraammine complex ratio during air calcination. For Pt/zeolite, the optimum calcination temperature is believed to be the minimum temperature necessary to attain complete decomposition of the starting complex ([Pt(NH,),12’>; this temperature is 300°C [30] and leads to maximum Pt dispersion. 4.2. The effect of dispersion on hydrogen solubility

I

I

[Pd(NH,),I’+

[Pd(NH,)2]2++

100

Co/d

Fig. 5. Solubility of hydrogen in Pd (Hb/Pdt) for catalysts prepared by ionic exchange from PdCl, and Pd(NO,), and by impregnation.

Figs. 5 and 6 quantitatively show the relation between absorbed hydrogen (H,) and dispersion for catalysts prepared by ionic exchange and by impregnation from Pd(NO,), or PdCl,. In both

J.H. Seplilveda, N.S. Fcgoli / Pd dispersion and hydrogen solubiliry in Pd /SO, 61

.

I

I

clx NO;

n

t

i

In$&natian

1 :

2 .A-

-~-_____-_r*--X-~

0

0

I

I

I

20

40

60

Dispersion Fig. 6. Solubility prepared

3’ I

80

100

(% 1

of hydrogen in Pd (H,/Pd,) for catalysts by ionic exchange and impregnation.

figures, solubility and dispersion values were taken from chemisorption data. As it can be seen in fig. 5 the solubility, defined as Ht,/Pd,, presents two zones: one tar dispersions higher than 40% (particles < 30 A), having a H,/Pd, ratio 0.36 and another with H,/Pd, > 0.36, for bigger particles. Other authors have also found that the solubility decreases for small particles [7,32] and Boudart and Hwang [8] predict H,/Pd, = 0 for D = 100%. The ratio H,/Pd, increases exponentially for dispersions higher than 80%; similar results have been found by Bonivardi 1331.The H,/Pd, ratio is constant for dispersions lower than 80%, in agreement with results reported by Boudart and Hwang [8], working with catalysts having dispersions between 12% and 73%. The high Hb/Pdb value: found in our results for small particles (d < 14 A) can be attributed to experimental errors, for example inadequate H, elimination. Considering that 30 min (step e during chemisorption) might be too long a time for H, elimination and that H,, might also be desorbed, experiments taking 10, 17 and 40 min were also performed. In the last two cases the isotherms were exactly the same; when only 10 min were taken, only 85% of H, was desorbed. The hydrogen TPD of catalysts having low and high metal dispersions clearly shows the desorption peak corresponding to absorbed hydrogen, as it can be seen in fig. 3. The absorbed hydrogen was also observed by TRS, and a good agreement

263

forWA-L

values exists between this method and chemisorption (see table 3). Consequently, the hydrogen absorption is correctly measured in our experiments. Jobic and Renouprez [341 have observed the hydride in Pd particles smaller than 15 A by neutron inelastic scatteritrg; Davis et al. [35] observed the same for 50 A particles by X-ray absorption spectroscopy, like Benedetti et al. [36] did for 28 A particles by TPR. The Pd particle size calculated from dispersion values assumes a certain particle shape; Perez et al. [37] have concluded that important errors in the calculation of particle size are introduced when using chemisorption values assuming simple geometric models. Assuming a sphere, the particle diameter is 11.57 A for 100% dispersion, and d= 11.57/D. According to Poltorak et al. [38], this diameter corresponds to 44 atoms, enough for the existence of bulk palladium. From calculations of the latter authors [38], assuming that 95% of the atoms are at the surface, the particle should have 19 atoms, 18 being at the surface and only one in the bulk. From these numbers, it is clear that the H,/Pd, values of our experiments, for small particles are physically impossible. Boudart and Hwang [8] suggested that one must distinguish between the different sorts of H, absorption in Pd (subsurface and bulk) in order to explain the effect of dispersion on hydrogen solubility. Konvalinka and Scholten [ 193 estimated the desorption energy for subsurface and a-phase hydrogen as 34 and 24 kJ/mol, respectively. According to our results and to those from the references, the high H,/Pd, ratio in small metal particles may be attributed to the presence of subsurface absorbed hydrogen and/or errors in particle size calculated from dispersion, assuming a simple sphere particle shape.

5. Conclusions The metal dispersion of Pd/SiO, catalysts prepared by ionic exchange is related to the calcination temperature. When the calcination temperature is lower than 300°C there still are ammine ligands joined to palladium; these species

264

.I.H. Sepdveda, N.S. Ffgoli / Pd dispersion and hydrogen solubility in Pd / 50,

have different mobilities and induce the formation of particles of different sizes. When the calcination temperature is higher than 500°C sintering occurs. The metal particle size has a strong influence on hydrogen solubility in Pd. In the case of H, solubility defined as Hr,/Pd,, this value is equal to 0.36 for high dispersions and higher than 0.36 for dispersions lower than 40%. The H,/Pd, is constant for dispersions up to 80%. Nevertheless, this value increases exponentially in very small particles due to the presence of subsurface absorbed hydrogen and/or important error in the calculation of particle size (d= 11.57/D) from dispersion, assuming a sphere.

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[15] T.-C. Chang, J.-J. Chen and C.-T. Yeh, J. Catal. 96 (1985) 51. [16] S.T. Homeyer and W.M. Sachtler, J. Catal. 117 (1989) 91. [17] J.S. Rieck and A. Bell, J. Catal. 85 (1984) 143. [18] R.J. Gorte, J. Catal. 75 (1982) 164. [19] J.A. Konvalinka and J.J.F. Scholten, J. Catal. 48 (1977) 374. [20] M. Kiskinova, G. Bliznakov and L. Surnev, Surf. Sci. 94 (1980) 169. 121) J.S. Rieck and A. Bell, J. Catal. 103 (1987) 46. [22] J.S. Rieck and A. Bell, J. Catal. 96 (1985) 88. [23] K.J. Leary, J.N. Michaels and A.M. Stacy, Langmuir 4 (1988) 1251. [24] H. Conrad, G. Ertl and E.E. Latta, Surf. Sci. 41 (1974) 435. [25] J.A. Konvalinka, P.H. Van Oeffelt and J.J. Scholten, Appl. Catal. 1 (1981) 141. [26] J.A. Konvalinka, J.J. Scholten and J.C. Rasser, J. Catal. 48 (1977) 365. [27] R.C. Weast, CRC Handbook of Chemistry and Physics, 58th ed. (CRC Press, Boca Raton, FL, 1977-1978). [28] S.T. Homeyer and W.M. Sachtler, J. Catal. 118 (1989) 266. [29] S.E. Wanke and P.C. Flynn, Catal. Rev.-Sci. Eng. 12 (1975) 93. [30] W.J. Reagan, A.W. Chester and G.T. Kerr, J. Catal. 69 (1981) 89. [31] R.A. Dalla Betta and M. Boudart, in: Proc. 5th Int. Congr. on Catalysis, Ed. J.W. Hightower (North-Holland, Amsterdam, 1973) p. 1329. [32] B. Moraweck, G. Clugnet and A. Renouprez, J. Chim. Phys. 83 (1986) 265. (331 A. Bonivardi, Doctoral Thesis, University National of Litoral, Argentina (1991). [34] H. Jobic and A. Renouprez, J. Less-Common Met. 129 (1987) 311. [35] R.J. Davis, S.M. Landry, J.A. Horsley and M. Boudart, Phys. Rev. B 39 (1989) 10580. [36] A. Benedetti, G. Fagherazzi, F. Pinna, G. Rampazzo, M. Selva and G. Strukul, Catal. Lett. 10 (1991) 215. [37] O.L. Perez, D. Romeu and M.Y. Yacaman, J. Catal. 79 (1983) 240. [38] O.M. Poltorak, V.S. Boronin and A.N. Mitrofanova, in: Proc. 4th Int. Congr. on Catalysis, Moscow, 1968, p. 68. [39] R.J. Cvetanovic and Y. Amenomiya, Adv. Catal. 17 (1967) 103.