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      Non-noble, efficient catalyst of unsupported α-Cr 2O 3 nanoparticles for low temperature CO Oxidation

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          Abstract

          Herein, we report the synthesis of chromium oxide nanoparticles, α -Cr 2O 3 NPs, followed by full characterization via XRD, SEM, XPS, and N 2 sorptiometry. The synthesized nanoparticles were tested as catalysts toward the oxidation of CO. The impact of calcination temperature on the catalytic activity was also investigated. CO conversion (%), light-off temperature, T 50, data were determined. The results revealed that chromia obtained at low calcination temperature (400 °C) is more active than those obtained at high calcination temperatures (600° or 800 °C) and this is ascribed to the smaller particle size and higher surface area of this sample. The results revealed a superior catalytic activity of Cr 2O 3 NPs at lower temperature as we reached a complete conversion at 200 °C which is high value in the forefront of the published results of other non-noble catalysts. The high activity of Cr 2O 3 nanoparticles (T 50 as low as 98 °C) where found to be dependent on a careful selection of the calcination temperature. These results may provide effective and economic solutions to overcome one of the major environmental threats.

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          Low-temperature oxidation of CO catalysed by Co(3)O(4) nanorods.

          Xiaowei Xie, Yong Li, Zhi-Quan Liu … (2009)
          Low-temperature oxidation of CO, perhaps the most extensively studied reaction in the history of heterogeneous catalysis, is becoming increasingly important in the context of cleaning air and lowering automotive emissions. Hopcalite catalysts (mixtures of manganese and copper oxides) were originally developed for purifying air in submarines, but they are not especially active at ambient temperatures and are also deactivated by the presence of moisture. Noble metal catalysts, on the other hand, are water tolerant but usually require temperatures above 100 degrees C for efficient operation. Gold exhibits high activity at low temperatures and superior stability under moisture, but only when deposited in nanoparticulate form on base transition-metal oxides. The development of active and stable catalysts without noble metals for low-temperature CO oxidation under an ambient atmosphere remains a significant challenge. Here we report that tricobalt tetraoxide nanorods not only catalyse CO oxidation at temperatures as low as -77 degrees C but also remain stable in a moist stream of normal feed gas. High-resolution transmission electron microscopy demonstrates that the Co(3)O(4) nanorods predominantly expose their {110} planes, favouring the presence of active Co(3+) species at the surface. Kinetic analyses reveal that the turnover frequency associated with individual Co(3+) sites on the nanorods is similar to that of the conventional nanoparticles of this material, indicating that the significantly higher reaction rate that we have obtained with a nanorod morphology is probably due to the surface richness of active Co(3+) sites. These results show the importance of morphology control in the preparation of base transition-metal oxides as highly efficient oxidation catalysts.
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            Chemisorption of CO and mechanism of CO oxidation on supported platinum nanoclusters.

            JUAN CAI, Ayman D Allian, Kyle L Fujdala … (2011)
            Kinetic, isotopic, and infrared studies on well-defined dispersed Pt clusters are combined here with first-principle theoretical methods on model cluster surfaces to probe the mechanism and structural requirements for CO oxidation catalysis at conditions typical of its industrial practice. CO oxidation turnover rates and the dynamics and thermodynamics of adsorption-desorption processes on cluster surfaces saturated with chemisorbed CO were measured on 1-20 nm Pt clusters under conditions of strict kinetic control. Turnover rates are proportional to O(2) pressure and inversely proportional to CO pressure, consistent with kinetically relevant irreversible O(2) activation steps on vacant sites present within saturated CO monolayers. These conclusions are consistent with the lack of isotopic scrambling in C(16)O-(18)O(2)-(16)O(2) reactions, and with infrared bands for chemisorbed CO that did not change within a CO pressure range that strongly influenced CO oxidation turnover rates. Density functional theory estimates of rate and equilibrium constants show that the kinetically relevant O(2) activation steps involve direct O(2)* (or O(2)) reactions with CO* to form reactive O*-O-C*=O intermediates that decompose to form CO(2) and chemisorbed O*, instead of unassisted activation steps involving molecular adsorption and subsequent dissociation of O(2). These CO-assisted O(2) dissociation pathways avoid the higher barriers imposed by the spin-forbidden transitions required for unassisted O(2) dissociation on surfaces saturated with chemisorbed CO. Measured rate parameters for CO oxidation were independent of Pt cluster size; these parameters depend on the ratio of rate constants for O(2) reactions with CO* and CO adsorption equilibrium constants, which reflect the respective activation barriers and reaction enthalpies for these two steps. Infrared spectra during isotopic displacement and thermal desorption with (12)CO-(13)CO mixtures showed that the binding, dynamics, and thermodynamics of CO chemisorbed at saturation coverages do not depend on Pt cluster size in a range that strongly affects the coordination of Pt atoms exposed at cluster surfaces. These data and their theoretical and mechanistic interpretations indicate that the remarkable structure insensitivity observed for CO oxidation reactions reflects average CO binding properties that are essentially independent of cluster size. Theoretical estimates of rate and equilibrium constants for surface reactions and CO adsorption show that both parameters increase as the coordination of exposed Pt atoms decreases in Pt(201) cluster surfaces; such compensation dampens but does not eliminate coordination and cluster size effects on measured rate constants. The structural features and intrinsic non-uniformity of cluster surfaces weaken when CO forms saturated monolayers on such surfaces, apparently because surfaces and adsorbates restructure to balance CO surface binding and CO-CO interaction energies.
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              Near-highway pollutants in motor vehicle exhaust: A review of epidemiologic evidence of cardiac and pulmonary health risks

              Doug Brugge, John Durant, Christine Rioux (2007)
              There is growing evidence of a distinct set of freshly-emitted air pollutants downwind from major highways, motorways, and freeways that include elevated levels of ultrafine particulates (UFP), black carbon (BC), oxides of nitrogen (NOx), and carbon monoxide (CO). People living or otherwise spending substantial time within about 200 m of highways are exposed to these pollutants more so than persons living at a greater distance, even compared to living on busy urban streets. Evidence of the health hazards of these pollutants arises from studies that assess proximity to highways, actual exposure to the pollutants, or both. Taken as a whole, the health studies show elevated risk for development of asthma and reduced lung function in children who live near major highways. Studies of particulate matter (PM) that show associations with cardiac and pulmonary mortality also appear to indicate increasing risk as smaller geographic areas are studied, suggesting localized sources that likely include major highways. Although less work has tested the association between lung cancer and highways, the existing studies suggest an association as well. While the evidence is substantial for a link between near-highway exposures and adverse health outcomes, considerable work remains to understand the exact nature and magnitude of the risks.
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                Author and article information

                Contributors
                Ali Bumajdad: a.bumajdad@ku.edu.kw
                Fakhreia Al Sagheer: f.alsagheer@ku.edu.kw
                Journal
                Journal ID (nlm-ta): Sci Rep
                Journal ID (iso-abbrev): Sci Rep
                Title: Scientific Reports
                Publisher: Nature Publishing Group UK (London )
                ISSN (Electronic): 2045-2322
                Publication date (Electronic): 1 November 2017
                Publication date PMC-release: 1 November 2017
                Publication date Collection: 2017
                Volume: 7
                Electronic Location Identifier: 14788
                Affiliations
                ISNI 0000 0001 1240 3921, GRID grid.411196.a, Chemistry Department, Faculty of Science, Kuwait University, P.O. Box: 5969, ; Safat, 13060 Kuwait
                Article
                Publisher ID: 14779
                DOI: 10.1038/s41598-017-14779-x
                PMC ID: 5665949
                PubMed ID: 29093548
                SO-VID: cff850ad-6708-4bc7-a1e4-a24b8ace86c5
                Copyright © © The Author(s) 2017
                License:

                Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

                History
                Date received : 25 January 2017
                Date accepted : 16 October 2017
                Categories
                Subject: Article
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                issue-copyright-statement © The Author(s) 2017

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