Carbonylation of Dimethyl Ether on Ag/ Cs1.5H1.5PW12O40: In-Situ FTIR Spectroscopy Study of the Ag-Carbonyls

Abstract

the catalyst. Moreover, iodide cocatalysts are carcinogens and they should be avoided in "green" chemistry. These problems may be overcome by developing a heterogeneous catalyst that can operate effectively without a halide promoter. Dimethyl ether (DME) is more favorable for carbonylation than methanol because it can be produced from syn-gas more effectively [2].Two types of acid catalysts are capable of activating C-O bonds in methanol or in DME: zeolites and heteropolycompounds. Starting with Cu mordenite [3] BP Chemicals Limited continued their discoveries in halide-free DME carbonylation with other acidic zeolites -H-ZSM5, and H-FER [4]. Wegman was the first to demonstrate that rhodium or iridium salts of tungstophosphoric heteropoly acid supported on silica can catalyze DME carbonylation to methyl acetate [5]. We subsequently have shown that acidic cesium salts of 12-tungstophosphoric acid promoted with rhodium can lead to a 10-fold enhancement in the activity of halide-free DME carbonylation to methyl acetate [6]. Recently we have observed that the addition of 1% of silver to Cs Here we report the characterization of silver carbonyl clusters on the surface of the acidic cesium salt of 12-tungstophosphoric acid using in situ FTIR spectroscopy. Experimental Catalyst preparationThe samples of Cs 1.5 H 1.5 PW 12 O 40 catalysts 1) unpromoted and 2) promoted with silver were prepared by the Abstract: Halide-free carbonylation of dimethyl ether (DME) to methyl acetate over heterogeneous catalysts offers a potentially green route to the production of important industrial chemicals. Previously we have shown that the addition of 1% of silver to Cs 1.5 H 1.5 PW 12 O 40 led to an increase in activity by a factor of two. Formation of silver carbonyl clusters on the surface of the catalyst was demonstrated by in situ FTIR spectroscopy. The v(CO) of silver carbonyl was observed at 2188 cm -1 and may be explained by the formation of cationic silver carbonyl Ag(CO) + on the surface of the acidic cesium salt of 12-tungstophosphoric acid. In view of the increased efficiency, the novel bifunctional catalyst Ag/ Cs 1.5 H 1.5 PW 12 O 40 is expected to hold significant promise for practical use in new processes of basic organic chemistry.

Dimethyl ether carbonylation over zeolites

“…NMR [22,[26][27][28] and IR [29] , revealed that, upon adsorption of methanol/DME, surface methoxy group was formed on the acidic OH group over the heteropolyacids, and CO insertion into the CH 3 -O bond resulted in the formation of acetate group attached to the Keggin anion. The promoting role of the noble metals was to adsorb CO from the gas phase and then transfer it to the surface CH 3 -O bond to form acetyls ( Fig.…”