Influence of the support on surface rearrangements of bimetallic nanoparticles in real catalysts

Abstract

Catalysts used for heterogeneous processes are usually composed of metal nanoparticles dispersed over a high-surface-area support. In recent years, near-ambient pressure techniques have allowed catalyst characterization under operating conditions, overcoming the pressure gap effect. However, the use of model systems may not truly represent the changes that occur in real catalysts (the so-called material gap effect). Supports can play an important role in the catalytic process by providing new active sites and may strongly affect both the physical and chemical properties of metal nanoparticles. We used near-ambient pressure x-ray photoelectron spectroscopy to show that the surface rearrangement of bimetallic (rhodium-palladium) nanoparticles under working conditions for ethanol steam reforming with real catalysts is strongly influenced by the presence of a reducible ceria support.

Hydrogen Production by Steam Reforming of Ethanol on Rh-Pt Catalysts: Influence of CeO2, ZrO2, and La2O3 as Supports

“…These results agree with oxidation/reduction cycles (Section 2.4.1) and may result from a change in the distribution of oxygen vacancies on the catalytic surface promoted by reducing agents present in the reaction system [68]. Divins et al [46] evaluated a RhPd/CeO2 catalyst in the SRE, also reporting an increase in the Ce +3 /Ce +4 ratio from 0.63 to 0.83 after reaction at 550 °C. The authors suggested that the capability of CeO2 as a support to activate water and to donate oxygen atoms could oxidize noble metals in the SRE.…”

“…In this way, some of the CO produced is converted to CO2 by the WGSR, which, as expected by thermodynamics, occurred to a lesser extent as the temperature increased (Table 1). Idriss et al [19] and Divins et al [46] evaluated RhPd/CeO2 catalysts in the SRE, reporting that the increase in H2 yield around 700 °C is due to simultaneous presence of WGSR and methane reforming.…”

IrPd nanoalloys: simulations, from surface segregation to local electronic properties

“…Concerning the Ir-Pd system, energy dispersive X-ray (EDX) profiles of the biggest particles (*5 nm of diameter) showed a surface enrichment in Pd (Zlotea et al 2014), as predicted by our calculations (in the experiments, the sensitivity of the EDX detector was not sufficient to allow recording of concentration profiles for small particles). Under reaction conditions, the structure may actually evolve (Divins et al 2014).…”

The influence of nano-architectured CeO supports in RhPd/CeO2 for the catalytic ethanol steam reforming reaction

“…To get insight into the structural characteristics of our RhPd/CeO 2 catalysts we have studied them by STEM and XRD under operando conditions. We have used operando XRD because we have recently shown that strong restructuring of the ceria-supported RhPd nanoparticles occurs under ESR conditions, which induces strong changes to the behavior of the catalyst [36]. about 15-25 nm in size and exhibiting abundant {1 1 1} crystallographic planes, as expected.…”