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

•Bimetallic catalyst (Pt-Pd, overall 0.5 wt.%) on sulfated zirconias were prepared.•They were tested for the gas-phase hydrodechlorination of different chloromethanes.•The catalysts showed high metal dispersion and stability.•The intrinsic activity increased with increasing metal particle size.•High overall dechlorination was achieved even with mixtures of four chloromethanes.

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%).

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