Characterization and activity study of the Rh-substituted pyrochlores for CO2 (dry) reforming of CH4

• Published in: Applied petrochemical research Vol. 3; no. 3-4; pp. 117 - 129
• Main Authors: Pakhare, Devendra, Wu, Hongyi, Narendra, Savinay, Abdelsayed, Victor, Haynes, Daniel, Shekhawat, Dushyant, Berry, David, Spivey, James
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-12-2013; Springer Nature B.V
• Subjects: Carbon dioxide; Catalysis; Chemistry; Chemistry and Materials Science; Energy Systems; Industrial Chemistry/Chemical Engineering; KACST-Forum; Lanthanum; Methane; Nanochemistry; Nanotechnology and Microengineering; Petrochemicals; Perovskite; Lanthanum zirconate; Pyrochlores; Lattice oxygen; Reverse water gas shift; Dry reforming; Isomorphic substitution
• ISSN: 2190-5525; 2190-5525
• DOI: 10.1007/s13203-013-0042-x

Isomorphic substitution of Rh at varying levels on the B site of lanthanum zirconate pyrochlore (La
2
Zr
2
O
7
; designated LZ) resulted in the formation of thermally stable catalysts suitable for fuel reforming reactions operating at 900 °C. Three specific catalysts are reported here: (a) unsubstituted lanthanum zirconate (LZ), (b) LZ with 2 wt% substituted Rh (L2RhZ), and (c) LZ with 5 wt% substituted Rh (L5RhZ). These catalysts were characterized by XRD, XPS, and H
2
-TPR. XRD of the fresh, calcined catalysts showed the formation of the pyrochlore phase (La
2
Zr
2
O
7
) in all three materials. In L5RhZ, the relatively high level of Rh substitution led to the formation of LaRhO
3
perovskite phase which was not observed in the L2RhZ and LZ pyrochlores. TPR results show that the L5RhZ consumed 1.57 mg H
2
/g
cat
, which is much greater than the 0.508 H
2
/g
cat
and 0.155 mg H
2
/g
cat
for L2RhZ and LZ, respectively, suggesting that the reducibility of the pyrochlore structure increases with increasing Rh-substitution. DRM was studied on these three catalysts at three different temperatures of 550, 575, and 600 °C. The results showed that CH
4
and CO
2
conversion was significantly greater for L5RhZ compared to L2RhZ and no activity was observed for LZ, suggesting that the surface Rh sites are required for the DRM reaction. Temperature programmed surface reaction showed that L5RhZ had light-off temperature 80 °C lower than L2RhZ. The spent catalysts after runs at each temperature were characterized by temperature programmed oxidation (TPO) followed by temperature programmed reduction and XRD. The TPO results showed that the amount of carbon formed over L5RhZ is almost half of that formed on L2RhZ.