Nanoparticle Exsolution from Nanoporous Perovskites for Highly Active and Stable Catalysts

Abstract

Nanoporosity is clearly beneficial for the performance of heterogeneous catalysts. Although exsolution is a modern method to design innovative catalysts, thus far it is predominantly studied for sintered matrices. A quantitative description of the exsolution of Ni nanoparticles from nanoporous perovskite oxides and their effective application in the biogas dry reforming is here presented. The exsolution process is studied between 500 and 900 °C in nanoporous and sintered La 0.52 Sr 0.28 Ti 0.94 Ni 0.06 O 3±𝜹 . Using temperature-programmed reduction (TPR) and X-ray absorption spectroscopy (XAS), it is shown that the faster and larger oxygen release in the nanoporous material is responsible for twice as high Ni reduction than in the sintered system. For the nanoporous material, the nanoparticle formation mechanism, studied by in situ TEM and small-angle X-ray scattering (SAXS), follows the classical nucleation theory, while on sintered systems also small endogenous nanoparticles form despite the low Ni concentration. Biogas dry reforming tests demonstrate that nanoporous exsolved catalysts are up to 18 times more active than sintered ones with 90% of CO 2 conversion at 800 °C. Time-on-stream tests exhibit superior long-term stability (only 3% activity loss in 8 h) and full regenerability (over three cycles) of the nanoporous exsolved materials in comparison to a commercial Ni/Al 2 O 3 catalyst.

Comparative Study of Exsolved and Impregnated Ni Nanoparticles Supported on Nanoporous Perovskites for Low-Temperature CO Oxidation

“…This behavior is in accordance with the lower surface Ni content estimated by H 2 -TPR. Furthermore, this confirms the sintering of exsolved Ni NPs during the reduction step at 800 °C, consistent with recent observations of Rudolph et al 31 Their findings suggest that at high reduction temperatures, Ni atoms rapidly diffuse to existing nuclei on the surface, promoting the growth of Ni NPs instead of forming new smaller ones. A prolonged reduction time of 800 °C clearly promotes the growth of Ni NPs.…”

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

“…The total cycle number in the present CL-DRM over Ni/WO 3 (10)/ZrO 2 is the highest among the previously reported CL-DRM systems (Table S2). − In another conventional DRM experiment performed at 750 °C, 1% CH 4 /1% CO 2 /He continuously flowed over Ni/WO 3 (10)/ZrO 2 . Initially, more than 99% of CH 4 and CO 2 were converted in conventional DRM (squares in Figure ); however, the conversions monotonically decreased with time.…”

“…The excessive emission of greenhouse gases (GHG) such as methane (CH 4 ) and carbon dioxide (CO 2 ) has become a global environmental problem. , CH 4 and CO 2 valorization, a favorable route to reduce GHG emissions, have been a subject of intense research. − Dry reforming of methane (DRM) is a promising catalytic reaction that can convert CH 4 and CO 2 to syngas (CO and H 2 ). ,− Although several efficient and durable catalyst systems for DRM have been developed recently, most reported catalyst systems suffer from certain drawbacks, such as catalyst deactivation due to coke deposition and undesired CO 2 reduction by the generated H 2 . Chemical looping dry reforming of methane (CL-DRM) has received considerable attention as an alternative technology to circumvent these drawbacks.…”

Segregation and interdiffusion processes in perovskites: a review of recent advances

“…Using TPD and XANES analyses for La 0.52 Sr 0.28 Ti 0.94 Ni 0.06 O 3± δ , it has been experimentally confirmed that a faster and greater release of oxygen in the nanoporous material results in twice as much Ni exsolution as in the sintered ceramics. 259 The high rate of oxygen exsolution also increases the nucleation kinetics of nanoparticles in SrTi 0.65 Fe 0.35 O 3− δ oxide, 260 Fig. 12A.…”