Support Induced Effects on the Ir Nanoparticles Activity, Selectivity and Stability Performance under CO2 Reforming of Methane.

Ersi Nikolaraki,Martin J Taylor,Kalliopi Kousi,Dimitris I Kondarides,Grammatiki Goula,Ioannis V Yentekakis,Georgios Kyriakou,Paraskevi Panagiotopoulou,Richard M Lambert

doi:10.3390/nano11112880

Abstract

The production of syngas (H2 and CO)—a key building block for the manufacture of liquid energy carriers, ammonia and hydrogen—through the dry (CO2−) reforming of methane (DRM) continues to gain attention in heterogeneous catalysis, renewable energy technologies and sustainable economy. Here we report on the effects of the metal oxide support (γ-Al2O3, alumina-ceria-zirconia (ACZ) and ceria-zirconia (CZ)) on the low-temperature (ca. 500–750 °C) DRM activity, selectivity, resistance against carbon deposition and iridium nanoparticles sintering under oxidative thermal aging. A variety of characterization techniques were implemented to provide insight into the factors that determine iridium intrinsic DRM kinetics and stability, including metal-support interactions and physicochemical properties of materials. All Ir/γ-Al2O3, Ir/ACZ and Ir/CZ catalysts have stable DRM performance with time-on-stream, although supports with high oxygen storage capacity (ACZ and CZ) promoted CO2 conversion, yielding CO-enriched syngas. CZ-based supports endow Ir exceptional anti-sintering characteristics. The amount of carbon deposition was small in all catalysts, however decreasing as Ir/γ-Al2O3 > Ir/ACZ > Ir/CZ. The experimental findings are consistent with a bifunctional reaction mechanism involving participation of oxygen vacancies on the support’s surface in CO2 activation and carbon removal, and overall suggest that CZ-supported Ir nanoparticles are promising catalysts for low-temperature dry reforming of methane (LT-DRM).

Highlights

In order to further study the Ir-catalyzed dry (CO2−) reforming of methane (DRM) reaction, in the present work, we focused on investigating low-temperature DRM performance at differential reaction conditions so as to decipher the role of metal-support interactions on the Ir intrinsic activity and selectivity by using supports with different values of oxygen storage capacity, namely γ-Al2 O3, ACZ (80 wt% γ-Al2 O3 – 20 wt% Ce0.5 Zr0.5 O2− δ ) and CZ (Ce0.5 Zr0.5 O2− δ )
It is worth noting that application of a reduction step directly after catalyst suspension drying was beneficial to the formation of small metallic Ir nanoparticles on the support surfaces [50,74,75], in contrast to methods which, instead of a reduction step at this stage of the preparation, use an oxidation one that results to the formation of larger Ir particles [78]
The dry reforming of methane to syngas production was investigated over Ir catalysts dispersed on three oxide supports (γ-Al2 O3, ACZ and CZ) characterized by different oxygen storage capacity (OSC)

Summary

Introduction

In light of the DRM energy applications, the produced syngas is a very suitable fuel for solid oxide fuel cells (SOFCs) operating at intermediate and high temperatures, or even, after CO removal, for lowtemperature polymer electrolyte membrane fuel cells (PEM-FCs), toward electrical power generation [3,4]. To this end, an enhanced electrical power efficiency and energy saving concept is the direct biogas-fueled solid oxide fuel cells (DB-SOFCs).

Methods

Results

Conclusion