Dialkyl carbonates have gained wide range of applications, owing to excellent chemical and physical properties. Pd-doped zeolites catalyzed Vapor-phase carbonylation reaction of methyl nitrite (MN) has been considered to be a more promising path to produce dimethyl carbonate (DMC). However, the effects of catalyst acidity nature and alkali metal promoters on catalytic properties are not fully clarified. In order to investigate the acidic nature of zeolite, Pd-doped NaY zeolites with varied SiO2/Al2O3 ratio were evaluated. They exhibited different catalytic activities, owing to the diverse acidic properties of NaY zeolite. Passivation with tetraethylorthosilicate, we further determined the the quantitative relationship between amount of Lewis acid sites and catalytic performances. A series of K-doped catalysts with different amount of potassium were investigated. The DMC selectivity on the basis of consumed methyl nitrite gradually increased, because that the amount of acid sites slowly decreased, as the NH3-TPD spectra indicated. The TOF (based on the CO conversion per mole Pd per hour) displays the shape of a volcano as the K-content increases. And the catalyst with 1wt.% K performed best. CO-adsorption FTIR results showed that the band representing CO adsorption downshifted and subsequently disappeared. This phenomenon could be attributed that CO was firstly activated by potassium and then the adsorption was hindered as an increase in the K-loading. In addition, XPS spectra illustrated that the Pd 3d peaks gradually drifted to lower binding energies with increasing the amount of potassium, directly related to the enhanced electron density of Pd sites. And these results further validate the phenomenon from CO-adsorption IR spectroscopy. On the basis of these findings, we deduce that adding a certain amount of potassium could activate CO, thus in turn improve the catalytic activities, while doping excessive amount of potassium will hinder CO adsorption and then reduce the catalytic activities. Moreover, the effect of different potassium precursors was also studied. And the experimental results indicated that the type of anion has some influence on the catalytic activity.

Alkaline-promoted Pd species catalyzed vapor-phase carbonylation of methyl nitrite to dimethyl carbonate

247th National Meeting (2014)

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