Kinetic and Spectroscopic Studies of Vinyl Acetate Synthesis Over Pd(100)

Abstract

A kinetic study of vinyl acetate (VA) synthesis over a Pd(100) catalyst is described, and the effect of particle-size on this reaction ascertained by comparing the single crystal data with data from supported Pd catalysts (5 wt% Pd/SiO 2 , d Pd =4.2 nm, and 1 wt% Pd/SiO 2 , d Pd =2.5 nm). A negative reaction order with respect to ethylene and a positive order with respect to oxygen were found for the model and supported catalytic systems, whereas the catalytic stability was strongly dependent on the particle size. The mechanism for VA synthesis is proposed to be identical on all catalysts studied based on the similarities of the kinetic parameters. Carbon-containing species on the poisoned Pd(100) catalyst were investigated by X-ray photoelectron spectroscopy (XPS), and the coverage was estimated to be approximately 1.5 ML after VA synthesis.KEY WORDS: kinetics of vinyl acehate synthesis; Pd(100) catalysts.

The nature of the active site for vinyl acetate synthesis over Pd–Au

“…The experiments were carried out in five ultrahigh vacuum (UHV) chambers equipped with XPS/LEISS [20], IRAS [20], high-resolution electron energy loss spectroscopy (HREELS) [21,22], or an XPS coupled to an elevated-pressure reactor [18,23]. Each chamber was also equipped with basic surface science techniques, Auger electron spectroscopy (AES), lowenergy electron diffraction (LEED) and a quadrupole mass spectrometer.…”

“…The VA synthesis experiments were carried out in a combined elevated-pressure reactor-UHV XPS chamber with a base pressure of 5 Â 10 À10 Torr [18,23]. The Au single crystal samples, Au(1 0 0) and Au(1 1 1), were attached via tantalum supporting wires for resistive heating, and were cleaned by argon sputtering followed by annealing at 950 K. The surface cleanness was verified with AES.…”

“…Acetoxylation of ethylene to vinyl acetate (VA) was selected as a probe reaction of Pd-Au bimetallic surfaces. Acetoxylation of ethylene on PdAu bimetallic silica-supported catalysts promoted with potassium acetate (KOAc) is a well-established commercial route for the synthesis of VA [3,5,[10][11][12][13][14][15][16][17][18].…”

Promotional Effects of Au in Pd-Au Catalysts for Vinyl Acetate Synthesis

“…Pd is an active catalyst for the acetoxylation of ethylene to vinyl acetate (VA), see equation (1) [2,3,[24][25][26][27][28][29][30][31][32][33][34][35][36]. However Pd is also an active catalyst for the combustion of ethylene and acetic acid and thus exhibits a low selectivity for VA synthesis (equations (2) and (3) 3) The addition of small amounts of Au to a supported Pd catalysts can significantly enhance its selectivity and activity for this reaction, as shown in Fig.…”

“…However Pd is also an active catalyst for the combustion of ethylene and acetic acid and thus exhibits a low selectivity for VA synthesis (equations (2) and (3) 3) The addition of small amounts of Au to a supported Pd catalysts can significantly enhance its selectivity and activity for this reaction, as shown in Fig. 1 [2,3,[28][29][30][31]. Silica supported Pd-Au bimetallic catalysts promoted with potassium acetate have been used as commercial catalysts for VA synthesis for more than 40 years.…”