Metal Micro-Monoliths for the Kinetic Study and the Intensification of the Water Gas Shift Reaction

Nuria García-Moncada,Francisca Romero-Sarria,Gianpiero Groppi,José Odriozola,Alessandra Beretta

doi:10.3390/catal8120594

Abstract

A kinetic study of the water gas shift (WGS) reaction has been carried out on a Pt-based catalyst promoted by a Zr-based proton conductor. The investigation was first performed on powders with diluted feed mixtures and then extended to more severe and representative conditions by using a catalyst coated metallic micromonolith. Temperature measurements reveal that isothermal conditions were obtained along the micromonolith during the tested conditions. In addition, the very thin catalytic layer allows for the discarding of intraporous resistances, providing excellent conditions to analyse the kinetics of the WGS reaction under the integral regime. The proposed rate expression accounts for independence on CO concentration, an inhibiting effect of H2 and a promoting effect of H2O; kinetic orders on CO and H2 are in line with those reported in the literature for the Pt-based catalyst. Instead, the obtained reaction order of water (0.36) is significantly lower than that reported for unpromoted catalysts (typically 0.77–1.10) in good agreement with the proposed water-enhancer effect of the proton conductor on the rate-limiting step. Metallic micromonoliths turn out to be a powerful tool for the kinetic investigation, due to the absence of mass and heat transport limitations and represent a strategy for the intensification of the WGS unit for future applications of fuel processors in small mobile devices.

Highlights

The determining role of water activation in the water gas shift (WGS) reaction over Pt-based catalysts is extensively accepted, since a significant influence of water pressure in the kinetics and positive reaction orders have been largely documented in the literature [1,2,3,4,5,6]
The kinetic analysis was performed at atmospheric pressure and at 80,000 mL·h−1 ·gcat −1 space velocity according to keep the reaction far from thermodynamic limitations in a sufficiently wide range of temperatures
The amount of PtCeAl catalyst in the reactor was maintained at 0.1 g with a mass ratio Cat/IC of 1:5 according to the previous studies [20]

Summary

Introduction

The determining role of water activation in the water gas shift (WGS) reaction over Pt-based catalysts is extensively accepted, since a significant influence of water pressure in the kinetics and positive reaction orders have been largely documented in the literature [1,2,3,4,5,6]. The promoter effect of a Zr-based proton conductor physically mixed with a typical Pt-based catalyst has been demonstrated previously in our group [18,19,20] These materials present oxygen vacancies capable of providing dissociated water and labile OH− species which enhance the proton conductivity and, the CO conversion. A proton conductor promoted catalyst is investigated by an extensive kinetic study, which aims at the development of a simple but representative rate expression, useful for future engineering applications. These may include both conventional synthesis gas treatments of the industrial chemistry, and novel small-scale applications of fuel processing for the feeding of proton-exchange membrane (PEM) fuel cells

Methods

Results

Conclusion