Acetylene hydrogenation on SiO2 supported gold nanoparticles

Acetylene hydrogenation has been investigated on 1.8 wt.% Au(I)/SiO2 and 1.9wt.% Au(II)/SiO2 catalysts prepared by fixation of Au sol to SiO2 (Aerosil 200). The mean particle size measured by TEM is 3.7 and 6.1 nm, respectively. For the sake of comparison a 2.1 wt.% Au/TiO2 sample was prepared by deposition-precipitation (DP) technique (mean particle size of Au is 3.3 nm). Transformation of acetylene was measured at 5 K/min ramp rate with gas mixtures containing the reactants at H-2/C2H2=2 and 70 ratios. The C2H2 content of the gas mixture was 0.11% (0.11 kPa C2H2). The activity sequence at 423 K was: Au/TiO2 > Au(I)/SiO(2)a parts per thousand << Au(II)/SiO2. Both the partial pressure of hydrogen and the temperature significantly affect the activity (acetylene conversion) and ethylene selectivity. Above 500-550 K over-hydrogenation (ethane formation) and hydrogenolysis (methane formation) decrease the ethylene selectivity. Faster deactivation and larger amount of deposit was observed on Au/TiO2 than on Au(I)/SiO2. A reaction scheme is proposed suggesting formation of sigma bonded intermediates as sp carbon hybridises to sp(2) and sp(3).