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

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.

Elucidation of Water Promoter Effect of Proton Conductor in WGS Reaction over Pt-Based Catalyst: An Operando DRIFTS Study

“…This fact indicates that Pt active sites are not strongly modified by the different feed. This supports the reported high CO coverages for Pt-based catalysts independently of the feeding conditions [58,61]. In this region is also observed bands at 2349 and 2143 cm −1 associated to gaseous CO2 and CO, respectively.…”

“…The increase of this band during the reaction indicates an increment of generated superficial carbon amount. This phenomenon could lead to the usual deactivation observed for these Pt/CeO 2 -based catalysts reported elsewhere [61].…”

Recent Advances in Structured Catalysts Preparation and Use in Water-Gas Shift Reaction

“…Monoliths are blocks consisting of parallel channels characterized by different shapes and sizes; ceramic monoliths, mostly made by cordierite and silicon carbide, are usually obtained by extrusion [9], two main designs are available, the flow-through configuration in which every channel is open on both side, and the wall-flow configuration in which the channels are alternatively closed, and the stream is forced to flow through the porous walls [10]. In the case of metal monoliths, the preparation techniques depend from the used alloy; in addition to extrusion, the rolling and the piling of crimped foils [5,[11][12][13] (Figure 2) and the perforated Lessing rings [14] allow to realize a wide variety of shapes and sizes of the channels. Metal monoliths exhibit higher mechanical strength and thermal conductivity, furthermore the possibility of creating thinner walls allows a higher cell density and lower pressure drops, with respect to the ceramic monoliths.…”

“…The latter species reacts with a hydroxyl group on a free platinum site, yielding CO 2 and H 2 O. Ceria, in fact, was found to reduce the activation energy of water, promoting its decomposition to hydrogen [77]. A kinetic analysis of the WGS reaction was also performed over a Pt/CeO 2 /Al 2 O 3 catalyst supported on a metallic (FeCr Alloy stainless steel) micro monolith [13]; in the latter case, the catalyst was promoted by a Zr-based ionic conductor. Catalytic experiments were performed between 200 and 400 • C; isothermal conditions through the monolith were verified within a very low error (4 • C), which is ascribable to the high thermal conductivity of the support.…”

“…Activity of different WGS structured catalysts. Parameters of the rate expression (Equation (2)) for the Pt/CeO 2 /Al 2 O 3 structured catalyst[13]. Activation energies of different WGS structured catalysts.…”