Stabilization and Au sintering prevention promoted by ZnO in CeOx–ZnO porous nanorods decorated with Au nanoparticles in the catalysis of the water-gas shift (WGS) reaction

• Published in: Journal of alloys and compounds 2022-02, Vol.892, p.162179, Article 162179
• Main Authors: de Oliveira, Cristine Santos, Teixeira Neto, Érico, Mazali, Italo Odone
• Format: Article
• Language: English
• Subjects: Catalysis; Catalysts; Catalytic activity; Cerium oxide; Cerium oxides; Copper; Gold; Gold nanoparticle; Hierarchical nanostructure; Leaching; Methanation; Nanomaterials; Nanoparticles; Nanoporous; Nanorods; Noble metals; Optimization; Reforming; Regeneration; Robustness; Shift reaction; Sintering; Sintering (powder metallurgy); Synthesis; Water purification; Water-gas shift; Zinc oxide
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2021.162179

•Novel porous CeO2–ZnO nanorods decorated with Au for WGS catalysis.•Acid lixiviation allowed controlled etching of CeO2 NR pores to better fit Au.•In CeO2–ZnO NR, ZnO forms a thin amorphous layer and some Zn(II) dopes CeO2.•Formation of smaller AuNP over CeO2–ZnO NR compared with CeO2 NR.•ZnO prevented Au sintering in WGS catalysis, even at 400–450 °C. [Display omitted] The addition of ZnO to CeO2 nanorods prior to AuNP decoration promoted the growth of smaller, well-distributed NP. The presence of ZnO also prevented AuNP sintering during catalysis of the water-gas shift reaction, even at higher temperatures, as seen from the stable catalyst activity. The development of CeO2-based nanomaterials for catalysis has seen considerable growth in the past decade, resulting of a combination of robust synthesis methods and its facile generation and regeneration of oxygen vacancy defects. Among its applications is the water-gas shift reaction (WGSR), used for purifying H2 from steam-reforming sources, where CeO2 combined with noble metal nanoparticles such as Cu, Au and Pt can present higher catalytical activity when compared to typical Fe-based or Cu/ZnO catalysts. In this work we designed a material for the catalysis of the WGSR seeking to address issues commonly observed for CeO2-Au catalysts: the optimization of the Au nanoparticle (AuNP) size and its maintenance by preventing sintering during catalysis, as well as preventing the formation of undesired side products such as CH4 and CH3OH. Our strategy was to combine a well-known, facile and robust hydrothermal synthesis to obtain CeO2 porous nanorods, and then further expand the native pore structure via a simple acid lixiviation strategy to better accommodate Au nanoparticles. To prevent side product formation, we coated the CeO2 nanorods with ZnO via metalorganic impregnation-decomposition prior to AuNP deposition, based on its reported ability to prevent methanation. While the formation of side products was prevented both with and without ZnO, we observed that ZnO promoted control over the growth of AuNP, resulting in smaller nanoparticles of 1.8 nm when compared to the 2.5 nm obtained without ZnO, and also prevented their sintering during WGSR catalytical tests, granting the material stable catalytic activity even at higher temperatures of 400 and 450 °C.