Ind. Eng. Chem. Res. 1989,28, 1752-1756
1752
the sodium samples. The presence of La also resulted in a decrease in the paraffin/olefin ratio in the product (Table VI).
Conclusions The large hydration energies of the trivalent La3+ion make the exchange of lanthanum ions with the acidic protons of ZSM-5 far more difficult than the exchange of monovalent sodium ions. Hexane adsorption experiments showed that, as with sodium exchange, lanthanum exchange does not decrease the effective free pore volume of the catalyst nor does it increase steric hindrances for the passage of linear molecules. Ammonia TPD showed that the presence of lanthanum ions leads to a decrease in the number of strong acid sites on the catalyst. This decrease is accompanied by an increase in the number of weak acid sites, suggesting that these ions function as weak acid sites when present on ZSM-5. Sodium exchange was shown to affect acidity in a similar way. The propene oligomerization and hexane cracking activity of H-ZSM-5 decreased with increasing degree of lanthanum exchange. This is due to the decrease in strong acidity resulting from the exchange. In the former reaction, the presence of lanthanum ions reduced the selectivity toward heavier products. Similar trends were observed for sodium-exchanged catalysts. The rate of catalyst deactivation during propene oligomerization was not reduced by the presence of lanthanum.
Acknowledgment The authors thank the University of Cape Town, Sasol, and the NEC for their financial assistance. Registry No. La, 7439-91-0; propylene (dimer), 16813-72-2; propylene (trimer), 13987-01-4; propylene (tetramer), 6842-15-5; propylene (pentamer), 15220-87-8; polypropylene, 9003-07-0; hexane, 110-54-3.
Literature Cited Anderson, J. R.; Foger, K.; Mole, T.; Rajadhyaksha, R. A.; Sanders, J. V. Reactions of ZSM-5 Type Zeolite Catalysts. J . Catal. 1979, 58, 114-130.
Argauer, R. J.; Landolt, G. R. US Pat. 3702886, 1972. Borade, R. B.; Hedge, S. G.; Kulkarni, S. B.; Ratnasamy, P. Active Centres Over HZSM-5 Zeolites for Paraffin Cracking. Appl. Catal. 1984, 13, 27-38. Buckley, R. G.; Tallon, J. L. Thermal Stability of ZSM-5. Chem. New Zealand 1986 (Feb), 11-12. Chang, C. D.; Silvestri, A. J. The Conversion of Methanol to Hydrocarbons Over Zeolite Catalysts. J. Catal. 1977,47, 249-259. Chang, C. D.; Chu, C.; Socha, R. F. Methanol Conversion to Olefins Over ZSM-5. J. Catal. 1984, 86, 289-296. Chen, N. Y.; Lucki, S.J. Low Temperature Hydrocarbon Conversion Over Rare Earth Exchanged Zeolite X Catalyst. Appl. Catal. 1988, 42, 169-180. Chiang, R. L.; Staniulis, M. T. PCT BO1-J, 29/06, ClOG, 11/05 1986. Derouane, E. G.; Nagy, B.; Dejaifve, P.; van Hoof, J. H. C.; Spekman, B. P.; Vedrine, J. C.; Naccache, C. Education of the Mechanism of Conversion of Methanol and Ethanol to Hydrocarbons on a New Type of Synthetic Zeolite. J. Catal. 1978, 53, 40-45. Fletcher, J. C. Q.; Kojima, M.; OConnor, C. T. Acidity and Catalytic Activity of Synthetic Mica Montmorillonite. Part 11: Propene Oligomerisation. Appl. Catal. 1986, 28, 181-191. Gabelica, Z.; Nagy, B.; Derouane, E. G.; Gilson, J. P. The Use of Combined Thermal Analysis to Study Crystallisation, Pore Structure, Catalytic Activity and Deactivation of Synthetic Zeolites. Clay Miner. 1984,19, 803-824. Garwood, W. E.; Stucky, G. D.; Dwyer, F. D. conversion of C2-C,, Olefins Over HZSM-5; ACS Symposium Series 218; American Chemical Society: Washington, DC, 1983; pp 383-396. Hill, S.G.; Arbuckle, R.; Seddon, D. Equilibrium Sorption of Paraffins in HZSM-5. Zeolites 1987, 7, 438-442. Lindsley, J. F. US Pat. 4,340,465, 1982. Miller, S. J.; Bishop, K. C. US Pat. 4,340,465, 1982. Olson, D. H.; Haag, W. 0.; Lago, R. M. Chemical and Physical Properties of ZSM-5 Substitutional Series. J . Catal. 1980, 61, 390-396. Owen, H.; Marsh, S. K.; Wright, S. B. US Pat 4,456,779, 1984. Shannon, R. D.; Vedrine, J. C.; Naccache, C.; Lefebure, F. Rhodium Exchange in Zeolites. J. Catal. 1984,88, 431-447. Tabak, S. A.; Krambek, F. J.; Garwood, W. E. Conversion of Propylene and Butylene Over ZSM-5 Catalysts. AZChE J. 1986,32, 1526-1531. Topsoe, N.; Pedersen, K.; Derouane, E. G. Infrared and Temperature Programmed Desorption Study of the Acidic Properties of ZSM-5 Type Zeolites. J. Catal. 1981, 70, 41-52. Wu, E. L.; Landolt, G. R.; Chester, A. W. Hydrocarbon Adsorption Characterisation of Some High Silica Zeolites. In New Developments in Zeolite Science and Technology; Murakami, Y., Lijima, A., Ward, J. W., Eds.; Elsevier: Amsterdam, 1986; pp 547-554.
Received f o r review April 3, 1989 Accepted August 23, 1989
Polymerization of Gaseous Benzyl Alcohol. 3. Deactivation Mechanism of a Si02/A1203Catalyst Martin Olazar, Andres T. Aguayo, Jose M. Arandes, and Javier Bilbao* Departamento de Ingenieria Quimica, Universidad del Pais Vasco, Apartado 644, 48080 Bilbao, Spain
The validity of the kinetic equation for the deactivation of a silica-alumina catalyst in the polymerization, under atmospheric pressure, of gaseous benzyl alcohol in a fluidized bed has been proven in the temperature range between 250 and 310 " C and for alcohol partial pressures up to 0.65 atm. The Langmuir-Hinshelwood-type kinetic equation has been deduced, the deactivation considered as a termination step in the polymerization, in which a growing polymer chain is irreversibly adsorbed and degraded to coke. From the mechanism, it is deduced that the deactivation occurs exclusively by active site blocking and not by pore blocking. In the same way, it has been proven that the coke remains chemisorbed as the reaction time increases. Obtaining polybenzyls from gaseous benzyl alcohol on acidic solid catalysts allows us to obtain these polymers with high thermal stability, with yields very much higher than those obtained by the traditional liquid-phase PO0888-5885/89/2628-1752$01.50/0
lymerization. In the first part of this work (Olazar et al., 1987a), the properties of the obtained polymers, the effect of the reaction conditions, and the behavior of the different Si02-A1,03 catalysts were studied. In the kinetic study
0 1989 American Chemical Society
Ind. Eng. Chem. Res., Vol. 28, No. 12, 1989 1753 Table I. Properties of Catalyst 1-35
S,, m2/g 286 70 A1203
12.3
V,, cm3/g
g/cm3 pa, g/cm3 Physical Properties 0.56 2.31 1.02 acidicity, mg n-butylaminelg catalyst pK +6.8 pK +4.8 pK +3.3 pK +2.8 Chemical Properties 48 35 26 23 P?,
carried out in the second part of this work (Bilbao et al., 1987a), it was proven that the polymerization before the deactivation of the catalyst is noticeable, that it followed a Langmuir-Hinshelwood-type mechanism, and that the corresponding kinetic equation fit the experimental data in the whole range of operating conditions (monomer concentration and temperature) possible in the laboratory. The validity of this kinetic equation was experimental evidence of the intervention of the catalyst active sites in a gas-phase polymerization reaction in the way usually accepted in contact catalysis. Thus, the validity of the theoretical postulates of Clark (1970), Clark and Bailey (1963a,b), and Maiti (1975) was experimentally proven. Besides the problems inherent in polymerizations on solid catalysts that condition the reactor design, all the catalysts tested for this reaction, silica-aluminas and Y zeolites, show rapid deactivation, which has its origin in the irreversible occupation of active sites by growing polymer chains. The hydrodynamic problems and the rapid deactivation require us to work in a catalyst circulation regime, consisting of fresh or regenerated continuous feeding and continuous withdrawal coated with polymer. Our original reactor was been set up in the "jet spouted bed" regime for this purpose (Bilbao et al., 1987b), where design of the kinetic equations that correspond to three steps, that is, initiation, developed polymerization, and deactivation, must be accurately known. The kinetic study of the deactivation is complex, due to the difficulties of the necessary experimentation as well as to the lack of existence of a method for data analysis for this type of reaction. In a first approach and in an empirical way, the activity vs time data were fit at a polymerization temperature of 270 OC to a first-order kinetic equation with respect to activity and to the partial pressure of benzyl alcohol (Bilbao et al., 1987a). Nevertheless, this equation, apart from not being based on any mechanism and not taking into account the intervention of the catalyst and of the reaction components through the deactivation, do not properly fit the experimental data for the whole range of working temperatures and of monomer concentrations. These limitations make it advisable to deduce a kinetic equation from the deactivation mechanism.
Catalyst and Reaction Conditions The catalyst used, named 1-35,is a silica-alumina whose preparation conditions were previously described (Olazar et al., 1987a). The properties are set out in Table I. The reaction equipment consists of a continuous feed and benzyl alcohol measuring system, a preheater, a 16-mm inside diameter reactor made of Pyrex glass, and a system for condensation and liquid product analysis by chromatography (Perkin-Elmer Sigma 3). The contact occurs in a fluidized bed. This regime must be used due to the characteristics of the polymerization, which is highly exothermic, and to the fact that the polymer is deposited, outwardly covering the catalyst particles. An acceptable isothermicity is obtained, diluting the catalyst with silica gel of the same particle size. The
'I
p=zp, t=xl" ----------
T
Figure 1. Scheme of the usual method for obtaining experimental Beginning of a reaction stage data, in four successive stages. (0) without external polymer. ( 0 )Stoppages in each stage.
20-
/
0
I
I
I
10
20
30
t (min ) Figure 2. Polymer evolution with time, at 270 O C . of stage 1. (0) Sequence of stage 2.
(X)
Sequence
operating conditions are as follows: catalyst particle size, 0.32-0.50 mm; space time, 0.4 (g of catalyst h)/mol; temperature, 250,270,290,310 "C; partial pressure of benzyl alcohol at inlet (diluted with NJ, 0.02,0.06,0.12,0.18,0.22, 0.30,0.40,0.50, and 0.65 atm; PAo,reaction time, 0.02 atm, 30-270 min; 0.06 atm, 10-160 min; 0.12 atm, 8-50 min; 0.18 atm, 2-38 min; 0.22 atm, 2-38 min; 0.30 atm, 2-38 min; 0.40 atm, 2-32 min; 0.50 atm, 2-32 min; 0.65 atm, 1-20 min. Under these conditions and with a gas velocity in the feed of 40 cm/s, an almost perfect mix is obtained for the solid, as long as the bed height, which increases as the reaction occurs, does not exceed 50 mm.
Kinetic Data Obtaining catalyst activity data for long periods of operation is difficult, due to the fact that the particles containing polymer knit together and consequently the fluidization is impeded. Thus, to get a datum corresponding to a long time, it is necessary to carry out several stages of short length where the ideal contact of plug flow is maintained. At the end of each stage, the polymer deposited outwardly on the catalyst particles is mechanically removed. I t must be taken into account that the polymer at room temperature takes on a powdery consistency and that it can be removed from the catalyst by vigorous knocking. In Figure 1, a scheme for obtaining the experimental data is shown, which generally has four successive stages. The total amount of polymer deposited is calculated by adding the polymer weights in the successive stages, and the total time is the sum of their lengths of time. In each stages, several stoppages of the reaction are carried out and the deposited polymer is weighed, with the aim of obtaining deposition data for different times. It was proven that, at the beginning of a new stage, the catalyst without an external coating of polymer had the same activity as at the end of the previous stage.
1754 Ind. Eng. Chem. Res., Vol. 28, No. 12, 1989 Table 11. Computed Values of t i (min) and r,. (g of Polymer/(g of Catalyst amin)) Pa.. atm 0.02 0.06 0.12 0.18 0.22 at 250 "C ti 25.1 9.7 5.8 4.3 3.4 PPO 0.22 0.68 1.17 1.4 1.5 12.2 6.4 at 270 "C ti 35.4 4.5 3.6 rPO 0.12 0.52 1.03 1.39 1.56 a t 290 "C 4 50.7 12.8 6.0 3.9 3.4 TP0 0.59 0.32 0.71 1.08 1.27 at 310 "C ti 75.5 16.5 6.9 4.4 3.4 rw 0.03 0.18 0.49 1.00 0.80
40
-
'
0.30
2.8 1.69 2.8 1.87 2.6 1.64 2.4 1.43
0.40 2.5 1.90 2.1 2.11 2.1 1.98 1.9 1.68
0.50 2.1 1.99 1.7 2.25 1.7 2.24 1.4 2.09
.
0 0
10
20
30
4Q
t
zw
2
L
6 2 0
LO
50
(min)
i l l 100
0.65 1.9 2.10 1.4 2.46 1.4 2.59 1.2 2.35
900
t (=In) t (mln) Figure 3. Deposited polymer against time, for different temperatures and partial pressures of benzyl alcohol fed to the reactor.
In Figure 2, deposited polymer vs time data have been plotted at 270 "C for three values of partial pressure for the benzyl alcohol feed. It is observed that, working with stages of different length, P-t data fit the same curve. This result make the following clear. Firstly, there is not a new initiation period in each stage, and the catalyst particles with growing polymer chains in their inside go to their activation state again, once the polymerization temperature is reached. Secondly, this result shows that the decrease in the activity with time is only a consequence of the deactivation of the catalyst and not of the possible resistance to the diffusion of the gaseous benzyl alcohol through the external polymer layer. It has been seen by experiments that such resistance does not exist, as was previously calculated from the study of the polymer structure, which is made up of 0.1-mm-diameter grains (Olazar et al., 1987b). In Figure 3, deposited polymer vs time data are shown for temperatures 250 and 310 "C. Each curve corresponds to one concentration of benzyl alcohol in the reactor feeding stream. It has been proven that the results of Figure 3, obtained in the fluidized bed and at operating intervals between which the polymer was removed, are practically equal to the results obtained when operating in the jet spouted bed regime, using equipment previously described (Bilbao et al., 1987b). The conical-cylindrical design of this equipment permits operation in an almost perfect mix regime
Figure 4. Values of polymerization rate against time, for different temperatures and partial pressures of benzyl alcohol fed to the reactor.
with longer operation times without hydrodynamic problems. The P vs t data corresponding to the four studied temperatures have been fit to the following empirical equation:
and where rh is the maximum value of the deposition rate per catalyst mass unit. From the fitting, the values of tiand rm set out in Table I1 have been calculated for each temperature and each partial pressure of the benzyl alcohol feed. The reaction rate can be defined as r = 1 dP (3) W d t , If the values of rh and ti,previously calculated and set out in Table 11, are substituted in eq 1 and if derivation as is defined in eq 3 is performed, the values of r p are obtained for the different temperatures and partial pressures of the alcohol feed. In Figure 4, the values of rp against time are shown as an example, for temperatures of 250 and 310 "C. In these plots, a short initiation period can be appreciated, where the polymerization rate increases very rapidly until the maximum, rpo, is reached. The catalyst deactivation subsequently causes a decrease in the
-(-)
Ind. Eng. Chem. Res., Vol. 28, No. 12, 1989 1755 polymerization rate, which is initially very rapid and which gradually attenuates with time. In order to appreciate in detail the values corresponding to the initiation period and to the beginning of the deactivation, two different scales have been established for the time in the x coordinates of some of these plots, using a break to separate them.
time and with partial pressure of benzyl alcohol at the reactor inlet has been obtained. The coke formation rate or the rate of the termination step by deactivation in the proposed mechanism is calculated as
Deactivation Mechanism Recently, kinetic equations for the deactivation by coke deposition have been obtained, which have been deduced from our previous knowledge of the main reaction mechanism and the coke formation considered as a consequence of additional steps to the mechanism (Corella and AsCa, 1982). In this way, kinetic equations are obtained that have the same parameters as the main reaction mechanism and those of the coke formation steps. The validity of these equations in a wide range of conditions has been proven, among other reactions, for the catalytic cracking in FCC units (Corella and Menbndez, 1986),disproportionation of cumene (Corella et al., 1986), dehydrogenation of benzyl alcohol (Corella et al., 1980; Romero et al., 1981), and decarbonylation of furfural (Srivastava and Guha, 1985). Since the deactivation is a termination step with irreversible occupation of active sites by growing polymer chains, which will suffer a degradation process to coke and possibly become inert, consequently causing deactivation by pore blocking, the steps proposed in our case are the following: 1. adsorption and deactivation step (initiation) M
+L
- KM
M,
k,
Defining the activity as
eq 5 is expressed in terms of the activity as
Expressing the monomer concentration in terms of the partial pressure of benzyl alcohol gives
M1*
where
where (4)
k', = k , ( 2 k , k , K ~ ~ ) ~ [ N ] ~ ~ - '
(9)
KM follows the following relation with temperature (Bilbao et al., 1987a) 9500 f 800 KM = 2.95 X ex,( (lo)
2. reaction step (propagation)
)
and in the studied reaction, we have
3. termination 3.1. spontaneous desorption
kd
M,* P, 3.2. desorption by monomer M,* 3.3. deactivation
+ M1 -!h.
bM,*
C,
P,
+L + L + M1
+ (b - l)L
In this last step, the parameter b indicates the number of polymer chains irreversibly adsorbed that end by occupying a catalyst active site.
Kinetic Equation of Deactivation From the postulated mechanism and following a development where the balance of the active sites is similar to that used for the deduction of the kinetic equation without considering the deactivation (at zero reaction time) (Bilbao et al., 1987a), the relation of catalyst activity with
Fitting the experimental data of Figure 4 (250 and 310 "C) and those corresponding to temperatures 270 and 290 "C by nonlinear regression (Marquardt, 1963) to eq 8, the values of the kinetic constant of deactivation have been calculated, which fulfill the following relation with temperature: 1O3OOTh 900) (12) k', = 5.27 X lo7 exp
(
The value calculated for the parameter b is unity. The deactivation equation can be expressed in an integrated way as 1 - 0.13r,a 2(0.13rPJ(1+ KMPb) In (1 - 0.13rp,Ja
+
(0.13r,)2 1- a 1 - 0.13r, 1 - 0.13rp0a
+ (1 + KMp&,)2-1 a- a 2 [N] k,kPk,KM2Pb2t (13)
In Figure 5, the values of the activity calculated with eq 13, solid lines, together with the experimental values, dashed lines, have been plotted at 250 and 310 "C and at
1756 Ind. Eng. Chem. Res., Vol. 28, No. 12, 1989 p = polymer weight, g
0 0 06 \,
,P,o:002atm
!00
0
200 t(min)
0
10
20
30
t (min)
PA= average partial pressure of benzyl alcohol between the inlet and the outlet of the reactor, atm P , = partial pressure of benzyl alcohol at the inlet of the reactor, atm P, = polymer of n monomer units R = deactivation rate, total number of monomer units in the polymer that are irreversibly adsorbed by unit catalyst weight and by unit time rpo,r , = polymer formation rates at t = ti and t > ti, respectively, g of polymer g-' of catalyst min-' S,= surface area, m2 g-' T = temperature, K t , td, ti = time, reaction time from the initiation period, and initiation period, min V = pore volume, cm3 g-' = catalyst weight, g
d
Greek Symbols pa, pr = particle density and solid density of
04
0 06 3 2 012
I
Figure 5. Values of activity against time: (-1 calculated, eq 9; (- - -1 experimental, from the data of Figure 4.
five partial pressures of benzyl alcohol feed. The accuracy of the fit between calculated and experimental values can be seen in the whole range of operating conditions studied. Discussion The result of b = 1when fitting the experimental data of deactivation to the equation deduced from the assumed mechanism shows that each growing polymer chain irreversibly adsorbed cancels out one active site. Consequently, the nature of the deactivation is entirely by blocking active sites and not by blocking pores (in which case, b < 1). Moreover, the irreversibly adsorbed polymer, although degraded, does not become partially inert through the reaction time (in this case, b > 1 would be the result). On the other hand, the validity of a Langmuir-Hinshelwood mechanism is shown for the whole range of operating conditions. It is also proven that the behavior of the catalyst active sites in the gas-phase polymerization is similar either in the main reaction or in the deactivation to the behavior in the rest of the catalytic reactions where the mechanism has been widely established. Nomenclature a = catalyst activity defined as the ratio of reaction rates C, = irreversibly adsorbed polymer molecule of n monomer units (coke) FAo = molar flow of monomer at the reactor inlet, mol mi& KM= equilibrium constant of the desorption of the monomer on an active site k,, k d , k , = rate constants of deactivation, spontaneous desorption, a n d desorption by monomer, respectively k,' = parameter introduced by eq 9 k , = propagation rate constant k l = rate constant of monomer activation on the active site L = free active site M = monomer molecule M1 = adsorbed monomer molecule M1*, M2*, ..., M,* = active species, monomer, dimer, ..., polymer of n monomer units, respectively MA = molecular weight of the monomer M, = molecular weight of the structural unit of the polymer N = total number of active sites by unit weight n = number of monomer molecules in the polymer
the catalyst, kg
m-3 Registry No. A1203,1344-28-1;benzyl alcohol, 100-51-6; silica, 7631-86-9; coke, 7440-44-0.
Literature Cited Bilbao, J.; Olazar, M.; Arandes, J. M.; Romero, A. Polymerization of Gaseous Benzyl Alcohol. 2. Kinetic Study of the Polymerization and the Deactivation for a Si02/A1203Catalyst. Ind. Eng. Chem. Res. 1987a, 26, 1960-1965. Bilbao, J.; Olazar, M.; Romero, A.; Arandes, J. M. Design and Operation of a Jet Spouted Bed Reactor with Continuous Catalyst Feed in the Benzyl Alcohol Polymerization. Ind. Eng. Chem. Res. 1987b, 26, 1297-1304. Clark, A. T h e Theory of Adsorption and Catalysis; Academic Press: New York, 1970. Clark, A.; Bailey, G. C. Formation of High Polymers on Solid Surfaces. I. Theoretical Study of Mechanisms. J. Catal. 1963a, 2, 230-243. Clark, A.; Bailey, G. C. Formation of High Polymers on Solid Surfaces. 11. Polymerization of Ethylene on Chromium Oxide-Silica-Alumina Catalyst. J . Catal. 1963b,2, 241-247. Corella, J.; Asfia, J. M. Kinetic Equations of Mechanistic Type with Nonseparable Variables for Catalyst Deactivation by Coke. Ind. Eng. Chem. Process Des. Dev. 1982, 21, 55-62. Corella, J.; MenBndez, M. The Modeling of the Kinetics of Deactivation of Nonfunctional Catalysts with an Acid Strength Distribution in their Non-Homogeneous Surface. Application to the Deactivation of Commercial Catalysts in the FCC Process. Chem. Eng. Sci. 1986,41, 1817-1826. Corella, J.; Asfia, J. M.; Bilbao, J. Kinetics of the Deactivation of a 10% ( 2 ~ 4 . 5 %Cr203/AsbestosCatalyst for Benzyl Alcohol Dehydrogenation. Chem. Eng. Sci. 1980,35, 1447-1449. Corella, J.; MonzBn, A.; Butt, J. B.; Absil, R. P. L. The Modelling of the Kinetics of Deactivation of a Commercial Catalyst in the Reaction of Cumene Disproportionation. J. Catal. 1986, 200, 148-156. Maiti, M. M. Formation of High Polymers on Solid Surfaces: An Analysis of the Results of Clark and Bailey. J . Catal. 1975, 38, 522-524. Marquardt, F. W. An Algorithm for Least-Squares Estimation of Nonlinear Parameters. J . SOC.Ind. Appl. Math. 1963, 11(2), 431-441. Olazar, M.; Bilbao, J.; Aguayo, A. T.; Romero, A. Polymerization of Gaseous Benzyl Alcohol. 1. Study of SiOz/Al2O3Catalysts and Reaction Conditions. Ind. Eng. Chem. Res. 1987a, 26,1956-1960. Olazar, M.; Bilbao, J.; Romero, A.; Aguayo, A. T. Polimerizacidn sobre catalizadores Sdlidos. Parte 111: Incidencia en la cinBtica de las propiedades del catalizador. Afinidad 1987b,44,337-340. Romero, A.; Bilbao, J.; Gonzilez-Velasco,J. R. Calculation of Kinetic Parameters for Deactivation of Heterogeneous Catalysts. I n d . Eng. Chem. Process Des. Dev. 1981, 20, 570-575. Srivastava, R. D.; Guha, A. K. Kinetics and Mechanism of Deactivation of Pd-A120BCatalyst in the Gaseous Phase Decarbonilation of Furfural. J . Catal. 1985, 91, 254. Received for review March 2, 1989 Accepted August 4, 1989
