The effect of lanthanum promoter on the selectivity of Pd/zeolite-X in methanol synthesis

Choudary, B. M. ; Matusek, K. ; Bogyay, I. ; Guczi, L. (1990) The effect of lanthanum promoter on the selectivity of Pd/zeolite-X in methanol synthesis Journal of Catalysis, 122 (2). pp. 320-329. ISSN 0021-9517

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The promoting effect of various amounts of lanthanum on Pd/zeolite-X in enhancing selectivity in CO hydrogenation toward methanol/oxygenates has been investigated. The catalysts were characterized by temperature-programmed reduction, O2-H2 titration, and temperature-programmed desorption. The dispersion and H2 chemisorption of Pd/zeolite-X catalysts were almost unchanged on La promotion. The virtually unchanged chemisorption capacity of the Pd/zeolite-X catalysts on La promotion is attributed to the cationic exchange method adopted to introduce La after Pd introduction into the zeolites. The La2O3 formed during calcination was partially reduced during reduction with hydrogen due to its contact with palladium. PdLaOx entities formed thereby trigger the activation of coordinated CO/H2 and facilitate the hydrogenation of CO to methanol/oxygenates at low temperature. Thus, the Pd sites responsible for methanol synthesis are stabilized by La at low and high pressures. Dimethyl ether, dominant for low La content Pd/zeolite-X catalysts, may be ascribed to the acid sites developed, but other mechanisms cannot be ruled out. The effect of the zeolite matrix lies in the stabilization of PdLaOx entities, but otherwise it behaves in a similar fashion to other supports. The zeolite lattice, however, ensures the maintenance of small PdLaOx particles. The turnover frequency values obtained with the optimum La promotion on Pd/zeolite-X are consistent with the reported values observed on Pd/La2O3 catalysts. The zeolites are therefore potential alternative supports in the preparation of suitable bimetallic systems.

Item Type:Article
Source:Copyright of this article belongs to Elsevier Science.
ID Code:85984
Deposited On:07 Mar 2012 06:03
Last Modified:07 Mar 2012 06:03

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