Water gas shift reaction on carbon-supported Pt catalysts promoted by CeO2 (original) (raw)
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Platinum-Promoted Catalysis by Ceria: A Study of Carbon Monoxide Oxidation over Pt(111)/CeO2
The Journal of Physical Chemistry, 1994
The structure and reactivity of a series of Pt(l1 l)/ceria model catalysts have been studied as a function of ceria coverage and morphology. XPS and LEED data show that the method of preparation results in growth of disordered CeOz which converts to epitaxial (1 1 1)-oriented ceria upon annealing at >700 K. Submonolayer ceria coverages strongly promote the oxidation of CO. Most strikingly, the fully encapsulated Pt(11 1) wafer is a much more effective catalyst than the bare metal itself. Disordered encapsulating films are much more active than ordered films. The results are discussed in terms of Pt-promoted oxygen vacancy formation in ceria and the predicted relative reactivity of principal crystal faces of the oxide.
Fundamentals and Catalytic Applications of CeO2-Based Materials
Chemical reviews, 2016
Cerium dioxide (CeO2, ceria) is becoming an ubiquitous constituent in catalytic systems for a variety of applications. 2016 sees the 40(th) anniversary since ceria was first employed by Ford Motor Company as an oxygen storage component in car converters, to become in the years since its inception an irreplaceable component in three-way catalysts (TWCs). Apart from this well-established use, ceria is looming as a catalyst component for a wide range of catalytic applications. For some of these, such as fuel cells, CeO2-based materials have almost reached the market stage, while for some other catalytic reactions, such as reforming processes, photocatalysis, water-gas shift reaction, thermochemical water splitting, and organic reactions, ceria is emerging as a unique material, holding great promise for future market breakthroughs. While much knowledge about the fundamental characteristics of CeO2-based materials has already been acquired, new characterization techniques and powerful th...
Applied Catalysis A: General, 2015
Pt on ceria catalysts for water-gas shift (WGS) reaction were prepared by employing three ceria nanopowders synthesized with different processing techniques and having different surface area and porosities. Nano-Pt (~0.5-2 nm) was deposited in the vapor phase onto each of the three ceria supports by Reactive Spray Deposition Technology (RSDT). The catalysts were performance tested for the WGS reaction in the temperature range of 150-450 °C at a gas hourly space velocity (GHSV) of 13,360 hr-1. The structure-activity relationship for the ceria-based materials was studied. The most promising catalyst was Pt supported on mesoporous ceria with crystallite size of 5.8 nm and Brunauer-Emmett-Teller (BET) surface area of 187 m 2 /g. This configuration demonstrated complete CO conversion at 225 °C. The CO adsorption strength and the ability to dissociate H 2 O are the two main factors that determine the activity of a particular catalyst site for the water−gas shift (WGS) reaction. This study leads to the conclusion that the highest water-gas shift reaction activity was obtained on Pt supported on the mesoporous ceria with low crystallite size and high surface area, with well dispersed Pt, leading to enhanced Ptceria interaction.
Journal of Catalysis, 2005
Partial reduction of ceria generates catalytically active bridging OH groups on the surface of ceria. Pt facilitates this surface reduction process, and in this work, the impact of the Pt promoter loading on catalyst structural-property relationships was explored. XANES spectra were recorded under H 2 treatment for a series of Pt/ceria catalysts with increasing Pt loading at both the Pt and Ce L III edges. Reduction of Pt oxide was hindered by metal-support interactions, such that higher Pt loadings facilitated reduction of Pt oxide to Pt 0 . Two routes of bridging OH group formation are as follows: (1) once it is reduced, Pt 0 dissociates H 2 , which spills over to the ceria surface to generate the bridging OH group active sites directly, accompanied by a change in the oxidation state of the Ce atoms involved with the sites from Ce 4+ to Ce 3+ ; and (2) H 2 or CO removes ceria surface capping oxygen atoms to generate vacancies (and surface Ce 3+ ), followed by H 2 O dissociation at the vacancies to generate the bridging OH groups. Either route highlights the direct link between the extent of ceria partial reduction and the active site density of the bridging OH group active sites. The relative Ce 3+ and Ce 4+ concentrations from XANES were quantified and at low temperature; the greatest degree of ceria reduction was obtained for the Pt/ceria catalysts with higher Pt loadings, correlating with a higher bridging OH group active site density. Using in situ DRIFTS, we used CO as a probe molecule, as it reacts with the bridging OH groups to generate surface formates, the proposed intermediates of the WGS reaction. While addition of CO to the unpromoted catalyst reduced at 250 • C led to only very weak formate bands due to a lack of bridging OH groups on the ceria surface at that temperature, strong formate bands arose on the surface of the Pt/ceria catalysts at 250 • C. In situ DRIFTS was also utilized to probe the dynamics of the surface formate coverages under low-temperature WGS reaction conditions over the Pt/ceria series. A high H 2 O/CO feed ratio was employed, and the surface formate coverages were found to be more limited by the WGS rate for the heavily loaded Pt/ceria catalysts. This indicates that Pt may not only serve to facilitate the generation of the bridging OH group active sites at low temperature, but may also be involved in accelerating surface formate decomposition, the elementary step of the mechanism that is proposed to be rate limiting. A clear trend of higher CO conversion with higher Pt loading was established in reaction testing. HR-TEM carried out on the 5%Pt/ceria catalyst indicated well-dispersed Pt clusters in the diameter range of 1-2 nm. 2004 Elsevier Inc. All rights reserved.
Water gas shift reaction over multi-component ceria catalysts
Applied Catalysis B: Environmental, 2012
This study reports the activity of ionic substituted bimetallic Cu-Ni-modified ceria and Cu-Fe-modified ceria catalysts for low-temperature water gas shift (WGS) reaction. The catalysts were synthesized in nano-crystalline size by a sonochemical method and characterized by XRD, TEM, XPS, TPR and BET surface analyzer techniques. Due to the ionic substitution of these aliovalent base metals, lattice oxygen in CeO 2 is activated and these catalysts show high activity for WGS at low temperature. An increase in the reducibility and oxygen storage capacity of bimetallic substituted CeO 2 , as evidenced by H 2 -TPR experiments, is the primary reason for the higher activity towards WGS reaction. In the absence of feed CO 2 and H 2 , 100% conversion of CO with 100% H 2 selectivity was observed at 320 • C and 380 • C, for Cu-Ni-modified ceria and Cu-Fe-modified ceria catalysts. Notably, in the presence of feed H 2 O, a reverse WGS reaction does not occur over these ceria modified catalysts. A redox reaction mechanism, involving oxidation of CO adsorbed on the metal was developed to correlate the experimental data and determine kinetic parameters.
Pt/Re/CeO2 Based Catalysts for CO-Water–Gas Shift Reaction: from Powders to Structured Catalyst
Catalysts
This work focuses on the development of a Pt/Re/CeO2-based structured catalyst for a single stage water–gas shift process. In the first part of the work, the activity in water–gas shift reactions was evaluated for three Pt/Re/CeO2-based powder catalysts, with Pt/Re ratio equal to 1/1, 1/2 ad 2/1 and total loading ≈ 1 wt%. The catalysts were prepared by sequential dry impregnation of commercial ceria, with the salts precursors of rhenium and platinum; the activity tests were carried out by feeding a reacting mixture with a variable CO/H2O ratio, equal to 7/14, 7/20 and 7/24, and the kinetic parameters were determined. The model which better described the experimental results involves the water–gas shift (WGS) reaction and CO as well as CO2 methanation. The preliminary tests showed that the catalyst with the Pt/Re ratio equal to 2/1 had the best performance, and this was selected for further investigations. In the second part of the work, a structured catalyst, obtained by coating a c...
Applied Catalysis A: General, 2005
The effect of CeO2 loading (1-20 wt.%) on the properties and catalytic behaviors of CeO2-Al2O3-supported Pt catalysts on the partial oxidation of methane was studied. The catalysts were characterized by SBET, Xray diffraction (XRD), temperature-programmed reduction (TPR) and oxygen storage capacity (OSC). XRD and TPR results showed that the pretreatment temperature of the support influences on the amount of CeO2 with fluorite structure. The pretreatment temperature of the support and CeO2 loading influenced the morphology of Pt. OSC analysis showed a significant increase in the oxygen storage capacity per weight of CeO2 for samples with high CeO2 loading (12 and 20 wt.%). TPR analyses showed that the addition of Pt promotes the reduction of CeO2. This effect was more significant for the catalysts with high CeO2 loading (≥12 wt.%). The dispersion of Pt, measured by the rate of cyclohexane dehydrogenation, increases with increasing of the pretreatment temperature of the support. It was shown that the kind of the support is very important for obtaining of catalysts resistant to carbon formation. The catalysts with high CeO2 loading (≥12 wt.%) showed the highest catalytic activity and stability in the reaction of partial oxidation of methane due to a higher Pt-CeO2 interface.
Improved CO-PROX Performance of CuO/CeO2 Catalysts by Using Nanometric Ceria as Support
Catalysts
Despite of the huge number of papers about the catalytic preferential oxidation of CO (CO-PROX) for the purification of H2 streams, there is still a need for more effective catalysts in order to reduce the large required catalyst volume of CO-PROX unity. In this work, large surface area nanometric ceria was used as support for CuO/CeO2 catalysts with CuO load up to 10 wt % easily dispersed by wet impregnation. Catalysts were characterized by ICP-MS, XRD, SEM/EDS, N2 physisorption, H2 temperature programmed reduction (TPR), and CO2 temperature programmed desorption (TPD) and tested under different reaction conditions (including under feed containing inhibiting species such as CO2 and H2O). Catalytic tests revealed that our samples show high activity and selectivity even under stringent reaction conditions; moreover, they result among the most active catalysts when compared to those reported in the scientific literature. The high activity can be related to the enhanced amount of highl...
Catalysis Letters, 2013
In this paper we demonstrate a way to prepare Pt/CeO 2 catalysts and test their catalytic activity in WGSR. The catalysts have been synthesized by a simple and low cost extractive-pyrolytic method. The temperature programmed reduction analysis revealed that the presence of platinum particles enhances the reduction degree of ceria. The morphology of the surface, the particle size and specific surface area were determined by TEM, XRD and BET analysis. EPR studies gave evidence of metal-support interaction, which increases the mobility of oxygen anions in crystal lattice. The effects of various operating parameters including the catalyst bed temperature, space velocity and feed H 2 O/CO ratio were also investigated. Subjecting the samples to pretreatment with H 2 or air had no strong effect on the catalytic activity. By varying the Pt loading, it was also found out that the maximum catalytic activity was achieved with the sample containing 1.2 wt% Pt, reaching up to 98 % CO conversion degree.
Synthesis and characterization of Pt/CeOx systems for catalytic CO oxidation reaction
Annales UMCS, Chemistry, 2011
Four different ceria supported catalyst were prepared by impregnation method with Pt(NO 3 ) 2 solution. The two supports are commercially available (MaTeck) and the other two were prepared by precipitation and microwave assisted hydrothermal method (MAH) respectively. The phase composition and average crystallite size of the catalysts were characterised with XRD technique. Finally the catalytic activity in CO oxidation reaction were determined in plug flow reactor in temperature range 300-900 K with 1 K resolution. The catalysts obtained in both precipitation and MAH methods exhibit catalytic activity at room temperature whereas catalysts obtained on MaTeck supports are not active at those conditions. In turn, catalysts based on MaTeck support are more active in temperature range 420-700 K. The different activities are attributed to difference in average crystallite sizes and in support morphology. ♣ This article is dedicated to Professor Dobiesław Nazimek on the occasion of his 65 th birthday