(600r) A Novel Bimetallic Catalyst for the Oxidative Esterification of Aldehyde | AIChE

(600r) A Novel Bimetallic Catalyst for the Oxidative Esterification of Aldehyde

Authors 

Sun, W. J., Tianjin University


Abstract:

The
direct oxidative esterification of methacrolein (MAL) with methanol to methyl
methactylate (MMA) process [1, 2] in the presence of molecular oxygen and a
catalyst under mild conditions has been developed in our laboratory. In
contract to the widely used acetone cyanohydrin (ACH) process [3], it is an
environmentally benign, and therefore the catalyst preparation is the key technology.
As for the esterification is reversible reaction, the generated water not only
impedes the forward chemical reaction but also forms a water film to retard the
diffusion of reactants to active sites [4], the hydrophobic material
styrene-divinylbenzene copolymer (SDB), with spherical architecture and inner
abundant pores, was used for the reaction. Early work demonstrated that the
monometallic Pd supported on SDB show higher catalytic performance than the
hydrophilic catalysts supported on SiO2 and ¦Ã-Al2O3
with MMA selectivity at 54 % and MAL conversion at 44 % [5]. However, MMA yield
was not sufficient because of the oxidation of the metal and occasionally this
caused a severe leaching of the metal into the reaction medium.

In the present work, in order to enhance the
catalytic performance and further studied the reaction mechanism, a new bimetallic
hydrophobic catalyst was prepared. The catalysts were prepared by incipient
wetness impregnation method and preparation conditions of the catalyst were studied.

The catalysts using hydrogen as reduction reagent
showed higher catalytic performance in the MMA selectivity and MAL conversion
for the reaction. Correspondingly, the catalyst reduced by hydrogen shows
higher surface area and smaller Pd particle size to form a fine dispersion of
Pd, which is favorable to the catalytic performance, compared with catalyst
using the methanol-formaldehyde as reduction reagent. Baed on the experimental
temperatures from 150 °æ to 250 °æ,the
catalytic performance peaks at the reduction temperature of 200 °æ.The reduction time was also
discussed from 2 h to 14 h and Pd(Cl)2 was reduced completely after 10
h according to XRD patterns.

The influence of lead was also investigated and the
experimental results demonstrate that varying the amount of Pb (from 0 to 2 wt
% at the interval of 0.5 wt %) change the catalytic activity and 0.6 wt % Pb
loading is the optimum in the highest MMA selectivity (86%) and MAL conversion
(79%) for the reaction. Compared to the monometallic catalyst (Pd/SDB), the
bimetallic catalyst (PdPb/SDB) show higher catalytic activity because  catalyst particles are better dispersed
on the support with smaller particle size and Pd-Pb atoms formed intermetallic
Pd3Pb1 crystals.

Moreover,
the investigation on reaction kinetics provides a useful tool for large-scale
direct production of MMA with higher performances over the hydrophobic
catalysts and the estimated order of the oxidative esterification is 2.1. The
reaction mechanism was also proposed. The selectivity of MMA of the reaction
over the monometallic Pd catalyst is lower than that of the Pd-Pb bimetallic
catalyst is due to the production of CO2 and we can conclude that
the atom Pd has relatively strong adsorption with O2. The influence
of the promoter, Pb, for the oxidation esterifiction, has weaken the
interaction of Pd and oxygen atom and then decreased the formation of CO2.
We concluded that the promoter of Pb has an optimal amount and it affects the
oxide species concentration directly which plays the critical role on the
selectivity of the catalyst. The experimental results demonstrate that the bimetallic
hydrophobic catalysts make the esterification reaction more efficient and
provide widely use in the reaction involving water as a product or reactant.

References-

[1] S. Yamamatsu, T. Yamaguchi, K.
Yokota, O. Nagano, M. Chono, A. Aoshima, Catal. Surv. Asia. 14 (2010) 124.

[2] H. Okamoto, H. Goto, Eupropean
P
atent 0 890 569 (2003), to Asahi Kasei Kabushiki Kaisha Osaka-shi.

[3] J. J. Spivey, M. RGogate, J.
RZoeller, R. DColberg, Ind. Eng. Chem. Res. 36 (1997) 4600.

[4] T.B. Lin. D.L. Chung, J.R. Chang, Ind. Eng. Chem. Res. 38
(1999) 1271.

[5] B.H. Wang, W.L. Ran, W.J. Sun, and K. Wang. Ind. Eng. Chem. Res. 51
(2012) 3932.

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