Effect of the Pt–Pd molar ratio in bimetallic catalysts supported on sulfated zirconia on the gas-phase hydrodechlorination of chloromethanes

Abstract

Bimetallic Pt:Pd catalysts with different molar ratios and 0.5 wt.% overall metal load supported on sulfated zirconia catalysts were synthesized and tested in the gas-phase hydrodechlorination (HDC) of chloromethanes and their mixtures. The catalysts were characterized by adsorption–desorption of N2 at −196 °C, X-ray diffraction, X-ray photoelectronic spectroscopy, temperature-programmed reduction, and aberration-corrected scanning transmission electron microscopy (STEM). The effect of the Pt:Pd molar ratio on the activity, stability, and selectivity was analyzed. The high acidity of the sulfated zirconia results in metal particles of small size (mainly <5 nm), as confirmed by STEM. The bimetallic catalysts showed higher stability than the monometallic ones, as demonstrated in long-term experiments (80 h on stream), confirming the positive effect of combining the two metallic phases. Turnover frequency (TOF) values in the range 0.0007–0.0168 s−1 and apparent activation energies between ≈41 and 44 kJ·mol−1 were obtained. TOF values for dichloromethane HDC increased with increasing mean metal particle size within the range of this work (≈1.2–2.3 nm). The catalysts with Pt:Pd molar ratios of 1:3 and 1:1 showed significantly better performance than the 3:1 one for overall dechlorination due to their higher atomic metal content and TOF at the same total metal weight load (0.5%).