I n d . E n g . Chem. Res. 1990, 29, 1766-1770
1766
Kinetics of Liquid-Phase Hydrogenation of Cinnamaldehyde over a Pt-Sn/Nylon Catalyst Enrico Tronconi* Dipartimento di Chimica Industriale e Ingegneria Chimica del Politecnico, P.zza L. Da Vinci 32, 20133 Milano, Italy
Carmelo Crisafulli Dipartimento di Scienze Chiniche, Uniuersitd di Catania, Viale A . Doria 6, 95125 Catania, Italy
Signorino Galvagno Dipartimento di Chimica Industriale, Uniuersitci di Messina, 98166 Villaggio S. Agata, Messina, Italy
Andrea Donato, Giovanni Neri, and Rosario Pietropaolo Facoltci di Ingegneria, Uniuersitd di Reggio Calabria, 89100 Reggio Calabria, Italy
The kinetics of liquid-phase hydrogenation of cinnamyl alcohol and cinnamaldehyde over Pt/nylon and Sn-Pt/nylon catalysts are investigated. Over both catalysts, hydrogenation of cinnamyl alcohol to hydrocinnamyl alcohol, methylstyrene, and propylbenzene is best described by a network of four parallel consecutive reactions with rate expressions assuming a single active site and saturation of cinnamyl alcohol. The kinetics of cinnamaldehyde hydrogenation over Sn-Pt/nylon in the range 10-60 " C are interpreted on the basis of a two-site model, where B sites, associated with Sn, are involved in hydrogenation of cinnamaldehyde and hydrocinnamaldehyde, whereas A sites, associated with Pt, catalyze cinnamyl alcohol hydrogenations. In line with independent chemical evidence, the results indicate strong adsorption of cinnamyl alcohol on Pt sites, which also explains the apparent negative activation energies of some rate constants.
Introduction The selective conversion of unsaturated carbonyl compounds into allylic alcohols is a difficult problem in heterogeneous catalysis. Due to the importance of unsaturated alcohols as intermediates in the preparation of various fine chemicals, several attempts have been made to develop a suitable catalytic system (Tuley and Adams, 1925; Rylander, 1967; Rylander and Steel, 1969; Millman and Smith, 1977; Rylander, 1979; Poscoe and Stemberg, 1980; Vanderspurt, 1980; Poltarzewski et al., 1986; Galvagno et al., 1986; Goupil et al., 1987; Giroir-Fendler et al., 1988; Galvagno et al., 1989; Vannice and Sen, 1989). Recently it has been reported (Poltarzewski et al., 1986; Galvagno et al., 1986; Galvagno et al., 1989) that addition of Sn to supported Pt catalysts modifies substantially their behavior in the liquid-phase hydrogenation of a,P-unsaturated aldehydes. The rate of hydrogenation was found to increase with increasing Sn/Pt ratio up to an optimal value, and then it decreased. The selectivity was also affected: while the preferential formation of saturated aldehydes was observed over Pt, the C=O bond was selectively hydrogenated over Pt-Sn catalysts, resulting in a,P-unsaturated alcohols. Similar results have been reported for addition to platinum of Fe3+,Zn2+,Ti4+,and Ge4+(Tuley and Adams, 1925; Galvagno et al., 1986; Goupil et al., 1987; GiroirFendler et al., 1988; Galvagno et al., 1989; Vannice and Sen, 1989). An enhanced rate of C=O bond hydrogenation has also been reported for addition of Cu to Ni-based catalysts (Noller and Lin, 1984) and of Sn and B to Ru (Narasimhan et al., 1988). Such effects appear to be associated with the formation of new catalytic sites, possibly involving promoter cations, which are able to coordinate the oxygen atom in the carbonyl group and to activate it. Accordingly, in the case of Pt-Sn catalysts the above results can be interpreted on the basis of a "two-site" mechanism, where Pt provides surface centers for the hydrogenation of unsaturated substrates, but electrophilic Sn ions constitute preferential sites for adsorption and activation of C=O groups which
are then easily reduced by hydrogen chemisorbed on the neighboring Pt sites. Very limited kinetic work has been published concerning the hydrogenation of unsaturated aldehydes. The kinetics of liquid-phase hydrogenation of 2-methyl-2-pentenal in n-hexane over several modified Raney cobalt catalysts were investigated by Hotta and Kubomatsu (1971,1972). It was found that two distinct Langmuir-type rate equations were required to describe the hydrogenation of the a,p-unsaturated aldehyde to 2-methylpentanol+ 2-methylpentanal and to 2-methyl-2-penteno1, respectively. This was interpreted as an indication that two different types of adsorbed 2-methyl-2-pentenal were involved in the hydrogenation reaction. Hotta and Kubomatsu's analysis, however, was confined to initial rate data. More recently, Niklasson and Smedler (1987) investigated the kinetics of the vapor-phase hydrogenation of 2-ethyl-2-hexenal on a Ni/SiO, catalyst. The best fit was provided by a mechanistic Langmuir-Hinshelwood model involving two distinct sites: one for C=C double-bond hydrogenation and one for hydrogenation of the carbonyl group. Independent adsorption studies also showed that a good part of the catalyst surface was saturated with almost irreversibly adsorbed aldehydes. In the following, a kinetic model for the liquid-phase hydrogenation of cinnanialdehyde over Sn-Pt/nylon catalysts is developed based on a "two-site" approach, and is then applied to the analysis of experimental rate data. Given the complexity of the reacting system, consisting of parallel and consecutive reactions, the hydrogenation kinetics of cinnamyl alcohol over Pt and over Pt/Sn catalysts have also been studied in order to obtain preliminary information on the reaction network. Experimental Section The kinetic experiments were performed on a Pt/nylon and on a Pt-Sn/nylon catalyst. Catalyst samples were prepared by impregnation of nylon powder, under nitrogen, with an ethanol solution of H,PtCl, and SnC1,. After filtration, the remaining solvent
0SSS-5S85/90/2629-1166~02.5~/0@ 1990 American Chemical Society
Ind. Eng. Chem. Res., Vol. 29, No. 9, 1990 1767 kI2
CALC k13
I@
5
HCALC
&
-
k34
MST
Q
PHP
Figure 1. Reaction network adopted for the kinetic analysis of the liquid-phase hydrogenation of cinnamyl alcohol over Pt/nylon and Pt-Sn/nylon catalysts.
was removed a t room temperature by evaporation under nitrogen flow and by drying under vacuum a t 343 K. Chemical analysis by atomic absorption gave a Pt content of 2.1 wt % for the monometallic samples and a Pt content of 1.2 wt % and a Sn content of 0.2 wt % for the multicomponent sample. Cinnamaldehyde (Fluka, purity >98%) and cinnamyl alcohol (Fluka, purity >97 %) were used after distillation under vacuum. Ethanol (Carlo Erba RPE-ACS 95%, analytical grade) used as solvent was employed without further purification. Hydrogenation of cinnamyl alcohol and cinnamqdehyde was carried out in a 100-mL four-necked flask, fitted with a reflux condenser, a thermocouple, and a dropping funnel. The catalyst was added to the required amount of solvent (25 mL of 95% ethanol) and then reduced a t 343 K for 1 h under Hz flow. After cooling at reaction temperature, the organic reactant (120 mg of cinnamyl alcohol or 95 mg of cinnamaldehyde) was injected through one arm of the flask. The reaction mixture was stirred with a stirrer head with permanent magnetic coupling (MEDIMEX) at a rate of 500 rpm, and the reaction was carried out a t atmospheric pressure under Hz flow. The progress of the reaction was followed by analyzing a sufficient number of microsamples withdrawn from the reaction mixture. Chemical analysis was performed with a gas chromatograph (Carlo Erba Model 4200) equipped with a flame ionization detector. The gas chromatograph column used was a 10% GP over SP2100. Quantitative analysis was carried out by calculating the area of the chromatographic peaks with an electronic integrator (Spectra Physics Model 4270). Preliminary runs performed with different amounts of catalyst and different stirring conditions showed the absence of external diffusional limitations. The original data used for the kinetic analysis are provided as supplementary material.
Results and Discussion 1. Hydrogenation of Cinnamyl Alcohol over Pt. The hydrogenation of cinnamyl alcohol (CALC) was performed in ethanol solvent at T = 60 “C using 0.2 g of 2.1% Pt/nylon catalyst. The major detected products included hydrocinnamyl alcohol (or phenylpropanol) (HCALC), phenylpropane (PHP), and P-methylstyrene (MST). Very small amounts of hydrocinnamaldehyde (HCALD) and of hydrocinnamaldehyde-diethyl acetal (DEA) were also detected but have been neglected in the analysis. HCALD is possibly originated by isomerization of cinnamyl alcohol. During their recent experiments of crotyl alcohol hydrogenation over Pt/A1203and Pt/TiOz catalysts, Vannice and Sen (1989) have also observed isomerization of the unsaturated alcohol to butyraldehyde, the rate of isomerization being, however, 1 order of magnitude slower than the rate of hydrogenation. The reaction scheme selected for the kinetic analysis is shown in Figure 1. Hydrogenation reactions of CALC to HCALC, PHP, and MST are envisaged as parallel pathways (steps 1, 2, and 3, respectively), MST being also
hydrogenated to P H P in a further consecutive step (4). The resulting network represented in Figure 1 involves four individual parallel and consecutive reaction steps. For a complete kinetic description of the reacting system, a total of four independent reaction rates has to be considered. The best fit of the data was obtained by assuming for each of the individual steps a rate expression of the type kijCi rij = (1) 1 + ~CALCCCALC Equation 1 is consistent with a Langmuir model where CALC tends to saturate the catalyst active sites, and Hz does not compete with CALC for adsorption onto the catalyst, as outlined in the following. Let us first consider the sites of the Pt catalyst associated with the activation of cinnamyl alcohol, and let us call them A sites. Assuming reversible competitive adsorption of cinnamyl alcohol (CALC) (because it is strongly adsorbed) and of the ethanol solvent (E) (becuase of its large excess) on A sites, neglecting the adsorption of the reaction products, and further assuming the sites to be saturated with the two adsorbates (Kishida and Teranishi, 1968), we write (2) OE + eCac = 1 where OE and OCm are the fractional coverages of ethanol and cinnamyl alcohol on A sites, respectively. Besides (3)
where C stands for the liquid-phase concentration and
gCm = AGad,CALC - AGadB is the difference of free energies
of adsorption on A sites between cinnamyl alcohol and ethanol. Assuming C E to be constant OCALC eE
6E =
- ~CALC~CALC
(4)
1
(5) 1+ ~CALCCCALC with UCALC = ( ~ / C Eexp(-gcALc/RT). ) Consider now, for example, reaction step 1 in Figure 1. If the surface reaction between cinnamyl alcohol, adsorbed on A sites, and hydrogen, adsorbed on different sites or still in the gas phase, is rate determining, the rate of reaction is given by rl = k’IZBCALCCH* (6) with CH*representing the concentration of activated Hz. In our experimental conditions, it is reasonable to expect that, CH*does not change significantly during the kinetic runs, so it can be incorporated into the rate constant. In this case, k’&H* = klz. Making use of (4) and (5) k1zacALcCcALc P1 = (7) 1 + ~CALC~CALC By similar reasoning
r4 =
k34aMSTCMST
1 + ~CALC~CALC
(10)
1768 Ind. Eng. Chem. Res., Vol. 29, No. 9, 1990 Table I. Optimal Estimatesa of the Kinetic Parameters for the Hydrogenation of Cinnamyl Alcohol* kl,acac, min" 0.640 f 0.449 k,,acac, mi+ 0.107 f 0.068 klracac, min-' 0.351 f 0.262 k3,aMsT,min" 0.494 f 0.317 ~ C A L CL/mol ~ 580.6 f 445.6
-
k02
HCALD
2b
ko'
1
3b lb
CALC
ethanol solvent over P t cata-
a With 95% confidence limits. lyst at T = 60 "C
:oncentrations
CALD
-
kl2
0
-
1
k22
HCALC
k 34
MST
mol/!
Q
PHP
Figure 3. Reaction network for the liquid-phase hydrogenation of cinnamaldehyde over the Pt-Sn/nylon catalyst.
0 0@90@
-
-ire
m--
Figure 2. Hydrogenation of cinnamyl alcohol over Pt/nylon in ethanol solvent, T = 60 OC. Comparison between experimental and calculated product concentrations. Rate parameters as in Table I.
An alternate explanation for eq 1 could be formally derived by (a) assuming that only CALC is adsorbed on A sites, ethanol and the other species being only weakly adsorbed, and (b) considering a fraction of free sites in the balance of A sites, Le., relaxing the saturation assumption. It is felt, however, that the great number of molecules per unit volume typical of the liquid phase, as well as the large excess of the ethanol solvent, let the treatment resulting in eqs 7-10 be preferred on a physical basis. Equations 7-10, containing five adaptive rate parameters, provide Langmuir-type rate expressions for the four individual steps of the reaction network in Figure 1. Values for the rate constants were determined by multiresponse nonlinear regression on the experimental C versus time profiles of the four major chemical species involved in the reaction. The corresponding calculated concentrations were obtained by integration of the following material balances: dCCALC/dt = -rl - r2 - r3 ~ C H C A L=Cri/ ~ ~ dCMsT/dt = r3 - r4 dCpHp/dt = r2 + r4
(11)
The resulting set of four ODES, eq 11, was integrated numerically with a standard Runge-Kutta-Merson algorithm with self-adjusting step size. The minimization of the weighted sum of squares of the residuals was performed by a specific optimization routine, based on several combined direct search procedures (Buzzi-Ferraris, 1970), which ensured quick convergence. Table I presents the optimal estimates for the five rate constants obtained at T = 60 "C. The goodness of fit for the concentrations of cinnamyl alcohol and of the three main reaction products is illustrated in Figure 2. The agreement is quite satisfactory: typical deviations correspond to mean absolute errors of few percents, which are comparable with the experimental
uncertainty. Using unit weights for all the experimental responses, since no estimate of their variance was available, we calculated a value of 1.067 for the MSE. A significantly greater error was obtained with a model assuming competitive adsorption of H2 and CALC on the same catalytic sites, as well as with other models based on different mechanistic assumptions. 2. Hydrogenation of Cinnamyl Alcohol over Pt-Sn. The liquid-phase hydrogenation of cinnamyl alcohol was investigated also over a Pt-Sn/nylon catalyst at T = 30 and 60 "C in order to test the general validity of the reaction scheme in Figure 1. The results of the catalytic runs were subjected to the same kinetic analysis presented in the previous subsection, and the following were found: (a) At both reaction temperatures, the data could be well represented by the same kinetic model which successfully described the product distribution obtained over the Ptonly catalyst. (b) At T = 60 "C, all the kinetic parameters were consistently smaller by about 1 order of magnitude than in the case of the Pt catalyst, reflecting the fact that the reactions were considerably slower over the Pt-Sn catalyst. Both results are consistent with the original hypothesis that the hydrogenation of cinnamyl alcohol, and the accompanying reactions illustrated in Figure 1, occur on catalytic sites associated with Pt (A sites), which are poisoned by addition of Sn. 3. Hydrogenation of Cinnamaldehyde over Pt-Sn. Catalytic runs for the hydrogenation of cinnamaldehyde over a Sn-Pt/nylon catalyst in ethanol were performed at T = 10, 30, 40, 50, and 60 "C. The reaction scheme adopted for the kinetic analysis of these data is shown in Figure 3. It represents an extension of the network previously developed to describe the hydrogenation of cinnamyl alcohol (Figure l ) , as it includes three additional steps (lb, 2b, and 3b) involving the hydrogenation of CALD to CALC and to HCALD, as well as the successive hydrogenation of HCALD to HCALC, respectively. Thus, a total of seven independent reaction rates are now to be considered for the kinetic description of the reacting system. As discussed above, hydrogenation of cinnamaldehyde and of hydrocinnamaldehyde does not occur on Pt-only catalysts. It appears then that the new pathways Ib, 2b, and 3b are strongly efihanced by the addition of Sn to the original Pt catalyst. We therefore assume that they occur on different catalytic sites (B sites) associated with Sn. For competitive adsorption of cinnamaldehyde and ethanol solvent on B sites, and under the same assumptions introduced for cinnamyl alcohol hydrogenation, the following rate expressions can be derived: = r2b
=
~OI~CALD~CALD
1+
~CALD~CALD
~O~~CALD~CALD
1+
~CALD~CALD
(13)
Ind. Eng. Chem. Res., Vol. 29, No. 9, 1990 1769 r3b
=
~ZZ~HCALD~HCALD
1 + ~CALDCCALD
with b c f i ~= ( ~ / C Eexp(-gCALD/Rn. ) The reacting system is now described by the following set of material balances:
2381 f 191 4388 f 193 9390 f 420
k1 = kOlbCfiD -3.127 f 0.060 k2 = k02bCaD -3.982 f 0.059 k3 = -6.832 f 0.098
dCcALD/dt = -rib - r2b dCHCALD/dt = r2b - r3b
k22bHCALD
k, = k,,acac k5 = kl,acfic kc = kllararr k"7 - k-MUMST -'-k, = aC-Cc kg = bCaDc
dCCALC/dt = r i b - r1 - r2 - r3 dCHCALC/dt = r3b + r 1 dCMST/dt = r3 - r4 dCPHP/dt = r2 + r4
Table 11. Optimal Estimates' of the Kinetic Parameters for the Hydrogenation of Cinnamaldehyde in Ethanol Solvent over the Pt-Sn Catalystb apparent activation energy rate constant ai Pi (Eapp), kcal/mol
(15)
The expressions for rates r l , r2,r3, and r4 are provided by eqs 7-10. Nine temperature-dependent rate constants are included in eqs 7-10 and 12-14. Each of them was assigned an Arrhenium-type expression ki = exp[ai - &(l/T - 0.003 25)] (16) In eq 16, 0.00325 is the reciprocal of the mean temperature of all observations. Reparametrization was adopted to avoid strong correlation between the estimates of ai and pi and to increase the rate of convergence of the regression procedure. This resulted in a total of 18 kinetic parameters, which were estimated by global multiresponse nonlinear regression on the 69 available measured concentrations of the six reacting species a t the five temperature levels. Table I1 presents the optimal estimates for the 18 kinetic constants. The goodness of fit of the calculated concentrations of cinnamaldehyde and of the five major reaction products to the experimental data is illustrated in Figures 4 and 5, corresponding to reaction temperatures of 10 and 60 OC, respectively. Similar results are obtained a t the intermediate temperatures. In all cases, the agreement is satisfactory, with typical deviations corresponding to mean percent errors in the range 3-1570. Table I1 also contains the apparent activation energies of the kinetic parameters. aCm and bCm exhibit negative temperature coefficients, indicating that CALC and CALD are more strongly adsorbed than ethanol on A sites and B sites, respectively. In particular, the large absolute value of gCALC, measuring the difference of free energy of adsorption between cinnamyl alcohol and ethanol, is supportive of a very strong adsorption of cinnamyl alcohol on A sites of the catalyst. Such a result is in good qualitative agreement with the findings of Bonnelle and co-workers (Hubaut et al., 1986a), who attributed the low monodihydrogenation selectivity observed in the hydrogenation of a-@ unsaturated aldehydes over copper chromite to the strong adsorption of the corresponding allylic alcohols. kOlbCALD, k02bCALD, and k22bHCALD exhibit a regular behavior, increasing with increasing temperature. On the other hand, k12acALc,k l 3 a c ~ ck, 1 4 a c ~ cand , kMamThave negative apparent activation energies. For the first three parameters, this unusual temperature dependence is related to the high adsorption energy of cinnamyl alcohol. Inspection of rate expressions (7)-(9) shows in fact that the actual activation energies of the rate constants k,,, k13, and k14 are obtained from the difference between their apparent activation energies and gCALC. Based on the estimates in Table 11, the true activation energies, shown in Table 111, are indeed positive, as expected. Values of about 10 kcal/mol for activation energies are in line with those reported for liquid-phase hydrogenation reactions
-2.164 -3.020 -2.274 -3.309 6.520 3.793
-9909 -8117 -9140 f 0.148 -3143 f 0.252 -14641 f 0.138 -3111 f 0.183 f 0.173 f 0.196
f 744 f 762 f 740 f 760 f 536 f 345
4.7 f 0.4 8.7 f 0.4 18.7 f 0.8 -19.7 -16.1 -18.2 -6.2 -29.1 -6.2
f 1.5
f 1.5 f 1.5 f 1.5 f 1.1 (Bcm)
f 0.7 (gem)
With 95% confidence limits. bRate expressions as in eqs 7-10 of L/ and 12-14. ki = exp[ai - & ( l / T - 0.00325)] min-'. mol. C o n c e n t r a t i o n s , mol/l
0.03000t CALO HCALO 0 CALC HCALC
F.,
b
0
0.02400
0.01800
I
b
0.01200 0.00600 0.00000
0
120 Time,
60
240
180 min
300
Figure 4. Hydrogenation of cinnamaldehyde over the Pt-Sn/nylon catalyst in ethanol solvent, T = 10 OC. Comparison between experimental and calculated product concentrations. Rate parameters as in Table 11. Concentrations,
mol/l
0.03000
m 0
0.02400
HCALD
10 CALC
HCALC
1
0.01200 0.00600 0.00000 0
60
120
180 Time,
240
300
360
min
Figure 5. Hydrogenation of cinnamaldehyde over the Pt-Sn/nylon catalyst in ethanol solvent, T = 60 O C . Comparison between experimental and calculated product concentrations. Rate parameters as in Table 11.
(Kishida and Teranishi, 1968). The negative apparent activation energy of k 3 , ~ M s T is explained on similar grounds. However, since no estimate of the free adsorption energy difference between MST and H2 is available in this case, the actual activation energy of k34 could not be calculated. Likewise, the lack of an estimate for ~ H C A L D prevented the evaluation of the actual activation energy of kzz.
1770 Ind. Eng. Chem. Res., Vol. 29, No. 9, 1990 Table 111. Estimates of the Actual Activation Energies for Some of the Rate Constants" rate constant Eatt,kcal/mol 10.9 f 1.1 ko1 14.9 i 1.1 k,, k12 9.4 f 2.6 13.0 f 2.6 k13 10.9 f 2.6 k14 "Calculated as Eatt= Eapp- g C f i D for for k 1 2 1 kX3, and k14.
kol.
&; as E,, = Eapp-
gCALC
Finally, it is worth mentioning that regression on the overall data was performed also by using a kinetic model incorporating competitive adsorption of CALD and H2 on B sites and of CALC and H2 on A sites. As in the case of hydrogenation of cinnamyl alcohol on the Pt/nylon catalyst, however, this model gave a significantly worse fit of the data than the present model, which assumes weak adsorption of H2on the active sites. Acknowledgment This work has been carried out with partial financial support of Progetto Finalizzato Chimica Fine e Secondaria 11. Registry No. CALC, 104-54-1; HCALC, 122-97-4; PHP, 103-65-1; MST,637-50-3; HCALD, 104-53-0; P t , 7440-06-4; Sn, 7440-31-5; cinnamaldehyde, 104-55-2.
Supplementary Material Available: Table S-I, listing raw kinetic data for the hydrogenation of cinnamyl alcohol over the Pt/nylon catalyst, and Table S-11, listing raw kinetic data for the hydrogenation of cinnamaldehyde over the SnPt/nylon catalyst (6 pages). Ordering information is given on any current masthead page. Literature Cited Buzzi-Ferraris, G. A n Optimization Method for Multivariable Functions. Presented at the Working Party on Routine Computer Programs and the Use of Computers in Chemical Engineering; Florence, Italy, 1970. Galvagno, S.; Poltarzewski, Z.; Donato, A.; Neri, G.; Pietropaolo, R. Selective Hydrogenation of a,@-UnsaturatedAldehydes to give Unsaturated Alcohols over Platinum-Germanium Catalysts. J . Chem. SOC.,Chem. Commun. 1986,1729. Galvagno, S.; Donato, A.; Neri, G.; Pietropaolo, R.; Pietropaolo, D. Hydrogenation of Cinnamaldehyde over Platinum Catalysts: Influence of Addition of Metal Chlorides. J. Mol. Catal. 1989,49, 223. Giroir-Fendler, A.; Richard, D.; Gallezot, P. Selectivity in Cinnamaldehyde Hydrogenation of Group-VI11 Metals Supported on Graphite and Carbon. In Heterogeneous Catalysis for Fine Chemicals; Guisnet, M., et al., Eds.; Elsevier: Amsterdam, The Netherlands, 1988.
Goupil, D.; Fouillox, P.; Maurel, R. Activity and Selectivity of PtFe/C Alloys for the Liquid Phase Hydrogenation of Cinnamaldehyde to Cinnamyl Alcohol. React. Kinet. Catal. Lett. 1987, 35, 185. Hotta, K.; Kubomatsu, T. Kinetics of Liquid-phase Hydrogenation of Alyphatic a,@-UnsaturatedAldehyde over Raney Cobalt Catalysts. Bull. Chem. SOC.Jpn. 1971,44, 1348. Hotta, K.; Kubomatsu, T. Kinetics of Liquid-phase Hydrogenation of Alyphatic a,@-UnsaturatedAldehyde over Raney Cobalt Catalysts Modified with Co-, Mn-, Ni-, and PdC1,. Bull. Chem. SOC. Jpn. 1972,45, 3118. Hubaut, R.; Daage, M.; Bonnelle, J. P. Selective Hydrogenation on Copper Chromite Catalysts. IV. Hydrogenation Selectivity for a,@-UnsaturatedAldehydes and Ketones. Appl. Catal. 1986a,22, 231. Hubaut, R.; Daage, M.; Bonnelle, J. P. Selective Hydrogenation on Copper Chromite Catalysts. V. Reactions of Allylic Alcohols. Appl. Catal. 1986b,22,243. Kishida, S.; Teranishi, S. Kinetics of Liquid-Phase Hydrogenation of Acetone over Raney Nickel Catalyst. J . Catal. 1968, 12, 90. Millman, W. S.; Smith, G. V. Role of Acetal Formation in Metal Catalyzed Hydrogenation and Exchange of Cinnamaldehyde. In Catalysis in Organic Syntheses; Smith, G. V., Ed.; Academic: New York, 1977; p 33. Narasimhan, C. S.; Deshpande, V. M.; Ramnarayan, K. Selective Hydrogenation of a,@Unsaturated Alcohols over Mixed Ruthenium-Tin Boride Catalysts. J. Chem. SOC.,Chem. Commun. 1988, 99. Niklasson, C.; Smedler, G. Kinetics of Adsorption and Reaction for the Consecutive Hydrogenation of 2-Ethylhexenal on a Ni/Si02 Catalyst. Ind. Eng. Chem. Res. 1987,26,403. Noller, H.; Lin, W. M. Activity and Selectivity of Ni-Cu/Al,O, Catalysts for Hydrogenation of Crotonaldehyde and Mechanism of Hydrogenation. J. Catal. 1984,85,25. Poltarzewski, Z.;Galvagno, S.; Pietropaolo, R.; Staiti, P. Hydrogenation of a,@-UnsaturatedAldehydes over Pt-Sn/nylon. J. Catal. 1986,102, 190. Poscoe, W. E.; Stemberg, J. F. Selective Hydrogenation of Unsaturated Aldehydes to the Corresponding Alcohols over a Rhenium Catalyst. In Catalysis in Organic Synthesis, 7th Conf., Jones, W. H., Ed.; Academic: New York, 1980; p 1. Rylander, P. N. Catalytic Hydrogenation ouer Platinum Metals; Academic: New York, 1967. Rylander, P. N. Catalytic Hydrogenation in Organic Syntheses; Academic: New York, 1979. Rylander, P. N.; Steele, D. R. Osmium Catalyzed Hydrogenations. Engelhard Ind., Tech. Bull 1969,10, 17. Tuley, W. F.; Adams, R. The Reduction of Cinnamic Aldehyde to Cinnamyl Alcohol in the Presence of Platinum-oxide Platinum Black and Promoters. XI. J. Am. Chem. SOC.1925,47, 3061. Vanderspurt, T. V. Supported Rhenium Selective Hydrogenation Catalysts and the Effect of CO and Cs2 thereon. In Catalysis in Organic Synthesis, 7th Conf.;Jones, W. H., Ed.; Academic: New York, 1980; p 11. Vannice, M. A.; Sen, B. Metal-Support Effecta on the Intramolecular Selectivity of Crotonaldehyde Hydrogenation over Platinum. J. Catal. 1989,115, 65.
Received f o r review December 29, 1989 Accepted May 2, 1990
