Operando Ce K-edge XANES Study of Low-loading Ni/CeO2 in Chemical Looping Dry Reforming of Methane

Abstract

In this study, operando Ce K-edge XANES measurements of CeO2-supported Ni (Ni/CeO2) catalysts for chemical looping dry reforming of methane (CLDRM) were performed. Low-loading Ni/CeO2 was effective for selectively promoting the partial oxidation of CH4 and suppressing coke deposition. Operando XANES measurements confirmed the redox state of Ce oxide in CLDRM and revealed that the reoxidation of reduced Ce oxide during CO2 reduction was faster than the reduction of Ce oxide during CH4 oxidation.

Chemical Looping Dry Reforming of Methane over Ni-Modified WO3/ZrO2: Cooperative Work of Dispersed Tungstate Species and Ni over the ZrO2 Surface

“…The resulting solid was dried overnight in an oven at 90 °C and then calcined at 500 °C in the air for 3 h. Ni-modified WO 3 -loaded metal oxides were synthesized similarly. In our previous study of CL-DRM using Ni-modified CeO 2 , higher Ni loading resulted in severe coke formation . To avoid the coke formation for investigation of the CH 4 partial oxidation over tungstate species and its redox reaction, we chose a very low Ni loading amount of 0.5 wt%.…”

“…Perovskite oxides − and hexaaluminates , require high reaction temperatures (>850 °C). Although Ni-modified CeO 2 has been recently studied as an effective material for CL-DRM at lower temperatures (approximately 750 °C) by several research groups, − OSMs for low-temperature CL-DRM need to be explored. In addition, the repetition of CL-DRM in previous studies was limited to a few dozen cycles, − and thus the long-term durability was rarely investigated.…”

“…Metal oxide-supported WO 3 , such as tungstated zirconia (WO 3 /ZrO 2 ) and tungstated alumina (WO 3 /Al 2 O 3 ), are widely used as heterogeneous acid catalysts for hydrocarbon isomerization and cracking and biomass conversions. − Their catalytic properties strongly depend on the structure of the WO 3 species, which is influenced by their surface W density estimated from the WO 3 loading amount and specific surface area. Isolated monotungstate and/or oligomeric polytungstate species are dominant in low surface W density (<4 W atoms/nm 2 ) whereas three-dimensional tungstate nanoclusters and/or monolayer domains are formed with the increase of surface W density increases to 4–8 W atoms/nm 2 .…”

“…In our previous study of CL-DRM using Ni-modified CeO 2 , higher Ni loading resulted in severe coke formation. 33 To avoid the coke formation for investigation of the CH 4 partial oxidation over tungstate species and its redox reaction, we chose a very low Ni loading amount of 0.5 wt%. For the preparation of the Ni/WO 3 (10)/ZrO 2 having mainly monoclinic phase (denoted as Ni/WO 3 (10)/ZrO 2 −monoclinic), Zr(OH) 4 (JRC-ZRO-6) was calcined at 500 °C for 3 h to synthesize monoclinic ZrO 2 .…”

What Is the Active Structure for High-Temperature Direct Dehydrogenative Conversion of Methane by the Supported NiP Catalysts─An in Situ XAFS Study

“…High-temperature XAFS experiments remain a challenge since the extended XAFS (EXAFS) oscillations damp rapidly as they are affected by the thermal disorder at high temperatures. 13 In situ X-ray absorption near edge structure (XANES) experiments have been reported for the Pt/CeO 2 14 and Ni/CeO 2 15 catalysts by observing the reduction of Pt site (Pt 4+ /Pt 0 ) and the reduction/oxidation cycle of Ce site (Ce 3+ /Ce 4+ ) over 1000 K under CH 4 atmosphere, but not reaching EXAFS range. Among the catalyst system, in situ XAFS experiments were usually conducted at the temperatures below 873 K. We previously were successful in conducting operando XAFS experiments for the In/SiO 2 catalyst under 1 atm methane flow at 1173 K, in which we could use the thick Xray window because In K-edge energy is up to 27 keV, 16 possessing high penetration ability through the matter.…”