Effect of reaction temperature on activity of Pt- and Ru-substituted lanthanum zirconate pyrochlores (La2Zr2O7) for dry (CO2) reforming of methane (DRM)

• Ru and Pt in the pyrochlore are the active sites for dry reforming of methane.
• Ru pyrochlore is more active toward DRM than Pt pyrochlore.
• This is the first ever study of the structure and activity of these materials for DRM.

Dry (CO2) reforming of methane (DRM) is a highly endothermic reaction (ΔH = +59.1 kcal/mol) producing syngas (H2 and CO) with the H2/CO ratio of ~1. DRM requires reaction temperatures above ~800 °C for complete equilibrium conversion to CO and H2, and is inevitably accompanied by carbon deposition. Here we examine lanthanum zirconate (La2Zr2O7) pyrochlores, with the larger trivalent cation La and a smaller tetravalent cation Zr occupying A and B sites, respectively. Three catalysts are tested: La2Zr2O7 [LZ] and two pyrochlores in which Zr in the B-site has been isomorphically partially substituted with (a) Ru (2.00 wt%) [LRuZ] and (b) Pt (3.78 wt%) [LPtZ]. The levels of substitution by weight correspond to identical atomic levels of substitution at the B-site. Here, activation energies are determined as a function of Ru or Pt substitution on the B-site. The results show that activation energies based on both CH4 and CO2 reaction rates are much lower for LRuZ than LPtZ. Conversion of CH4 (XCH4XCH4) and CO2 (XCO2XCO2) was greater for LRuZ compared to LPtZ at 525 °C, 575 °C, and 625 °C throughout an on-stream time of 600 min. After each 600-min run, temperature programmed oxidation (TPO) showed that total carbon formation decreased with increasing reaction temperature, although the stability of the deposited carbon increased with increasing reaction temperature.

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