Preparation and catalytic performance of Pd/CaCO3catalysts for low-temperature carbon monoxide oxidation.

To develop low-cost, high-performance catalysts for low-temperature carbon monoxide (CO) oxidation, a low-crystallinity calcite-type CaCO3support was prepared by calcining calcium citrate at 500 °C. Pd based catalysts with Pd loadings of 0.2-2 wt.% over the obtained CaCO3supports were synthesized via excess impregnation, using palladium acetate as the precursor and acetone as the solvent. The Pd/CaCO3catalysts were systematically characterized by XRD, N2adsorption-desorption, TEM, EDS and XPS, and their low-temperature CO oxidation performance was evaluated. All catalysts exhibit mesoporous features with Type IV isotherms and Type H3 hysteresis loops, and 0.5Pd/CaCO3displays the optimal specific surface area, pore volume and pore size. The average Pd particle size increases from 1.86 nm to 4.23 nm with rising Pd loading, and 0.5Pd/CaCO3possesses highly dispersed ultrafine Pd particles of 2.21 nm. The control sample 0.5Pd/precipitated CaCO3has aT100of 140 °C, while 0.5Pd/CaCO3achieves complete CO conversion at 120 °C and retains stable conversion over 120 h of continuous testing, verifying the advantage of the self-made support. The better performance for calcining samples arises from the synergistic effect of Pd0and Pd2+, highly dispersed Pd nanoparticles, a developed mesoporous structure and the defect anchoring effect. This study provides a scalable, low-cost and efficient Pd-based catalytic approach for low-temperature CO oxidation.