Platinum Based Catalysts in the Water Gas Shift Reaction: Recent Advances

Abstract

<jats:p>The water gas shift (WGS) is an equilibrium exothermic reaction, whose corresponding industrial process is normally carried out in two adiabatic stages, to overcome the thermodynamic and kinetic limitations. The high temperature stage makes use of iron/chromium-based catalysts, while the low temperature stage employs copper/zinc-based catalysts. Nevertheless, both these systems have several problems, mainly dealing with safety issues and process efficiency. Accordingly, in the last decade abundant researches have been focused on the study of alternative catalytic systems. The best performances have been obtained with noble metal-based catalysts, among which, platinum-based formulations showed a good compromise between performance and ease of preparation. These catalytic systems are extremely attractive, as they have numerous advantages, including the feasibility of intermediate temperature (250–400 °C) applications, the absence of pyrophoricity, and the high activity even at low loadings. The particle size plays a crucial role in determining their catalytic activity, enhancing the performance of the nanometric catalytic systems: the best activity and stability was reported for particle sizes &lt; 1.7 nm. Moreover the optimal Pt loading seems to be located near 1 wt%, as well as the optimal Pt coverage was identified in 0.25 ML. Kinetics and mechanisms studies highlighted the low energy activation of Pt/Mo2C-based catalytic systems (Ea of 38 kJ·mol−1), the associative mechanism is the most encountered on the investigated studies. This review focuses on a selection of recent published articles, related to the preparation and use of unstructured platinum-based catalysts in water gas shift reaction, and is organized in five main sections: comparative studies, kinetics, reaction mechanisms, sour WGS and electrochemical promotion. Each section is divided in paragraphs, at the end of the section a summary and a summary table are provided.</jats:p>

Performance Analysis of the Perhydro-Dibenzyl-Toluene Dehydrogenation System—A Simulation Study

“…The analysis shows an increase in metal loading (platinum) from 0.5 to 2 wt.% has led to an increase in the value of DoD, however, the further increase has led to a decrease in the degree of dehydrogenation, as shown for 5 wt.% catalyst. This is in agreement with the study by Palma et al [43], i.e., for the metal loading of 2 wt. %, there is a fine dispersion on the base surface with the least agglomeration, while the increase in metal loading from 2 to 5 wt.% has led to a comparative increase in the agglomeration, reduced dispersion, reduced metallic surface area, and reduced number of reducible species, thereby leading to reduced catalytic activity.…”

Main Hydrogen Production Processes: An Overview

“…In addition to carbon monoxide and hydrogen, in the gas stream at the outlet of the reformer, unreacted methane and carbon dioxide are also present, therefore, further treatment/purification steps are necessary for obtaining pure hydrogen. In particular, one [15] or two stages of CO-water gas shift [16,17] followed by selective methanation [18], preferential oxidation [19] or a treatment with permselective membranes [20]. Although noble metal-based catalysts provide high activity and good stability, the high cost and the limited availability of the noble metals prevent their use, so Ni/Al 2 O 3 is the most used commercial catalyst for MSR [21].…”

“…In solid oxide electrolysis cells (SOEC), a solid oxide or ceramic is used as electrolyte; at the cathode side hydrogen is produced from water (17), while the oxygen ions generated, across the electrolyte, reach the anode (16) where they are oxidized to produce oxygen: The solid oxide electrolysis cells typically operate in the temperature range 500-900 • C [177], which provides a crucial benefit over proton exchange membrane (PEM) and alkaline exchange membrane (AEM) electrolyzers, which operate at a maximum of 100 • C. Unfortunately, the degradation of SOEC is the major limitation to the commercial viability, the aggressive humid condition in the air electrode side, is still a concern to the stability of electrolysis cells [178]. Typically, Ni/yttria-stabilized zirconia (Ni/YSZ) electrodes are used [179], however agglomeration of Ni nanoparticles, low water vapor transmission efficiency and poor durability are serious issues [180].…”

Low Temperature Water-Gas Shift: Enhancing Stability through Optimizing Rb Loading on Pt/ZrO2

“…Interestingly, different mechanisms have been reported for nearly identical formulations in some cases (e.g., Pt supported on ceria-zirconia mixed oxides) [11,12]. In a recent review, Palma et al summarize the mechanisms proposed for many Pt-based catalysts in the recent literature [13]. In the review, the authors note that an associative mechanism was reported for all the alkali promoted Pt-based catalyst formulations investigated.…”