Role of metal substitution in lanthanum zirconate pyrochlores (La2Zr2O7) for dry (CO2) reforming of methane (DRM)

Dry (CO 2 ) reforming of methane (DRM) produces syngas with H 2 /CO ratio of ≤1. In this work, we report the use of pyrochlores (A 2 B 2 O 7 ) as catalysts for this reaction. Here, we examine lanthanum zirconate pyrochlores, LZ, with lanthanum and zirconium occupying the A and B sites, respectively. Three catalysts are tested: LZ and two pyrochlores in which the B-site has been isomorphically substituted with (a) Ru (2 wt%) (designated LRuZ) and (b) Pt (3.78 wt%) (designated LPtZ). These levels of substitution by weight correspond to identical atomic levels of substitution at the B-site. The effect of isomorphic substitution of Ru and Pt on the structure and activity of the pyrochlores in DRM is studied in this work. ICP-OES, XRD, H 2 and CH 4 TPR were used to characterize the structure of the catalysts. XRD results confirmed the formation of the La 2 Zr 2 O 7 phase in the bulk of the pyrochlores. H 2 TPR showed higher reduction temperatures for LPtZ compared to LRuZ, suggesting a less reducible, stable Pt in the pyrochlore structure compared to Ru. Quantitative analysis showed that LRuZ consumed 0.534 mg H 2 /g cat , whereas LPtZ consumed only 0.161 mg H 2 /g cat corresponding to much greater extent of reduction for LRuZ compared to LPtZ. CO formation during CH 4 TPR showed that both materials have reactive lattice oxygen which helps in reducing carbon formation during DRM. Temperature programmed oxidation studies of the catalyst immediately after CH 4 TPR showed greater carbon formation over LPtZ (1.67 g c /g cat ) compared to LRuZ (1.17 g c /g cat ) suggesting that Pt activates CH 4 to a greater extent compared to Ru. Temperature programmed DRM surface reaction showed that the light off temperature for LRuZ was about 45 °C lower than that of LPtZ. These are novel results and constitute the first report of which we are aware for Pt and Ru substituted pyrochlores for DRM.