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Guilhaume N, Bianchi D, Wandawa RA, Yin W, Schuurman Y. Study of CO2 and H2O adsorption competition in the combined dry / steam reforming of biogas. Catal Today 2021. [DOI: 10.1016/j.cattod.2020.04.058] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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2
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Giraud F, Geantet C, Guilhaume N, Loridant S, Gros S, Porcheron L, Kanniche M, Bianchi D. Individual amounts of Lewis and Brønsted acid sites on metal oxides from NH3 adsorption equilibrium: Case of TiO2 based solids. Catal Today 2021. [DOI: 10.1016/j.cattod.2020.08.015] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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3
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Couble J, Buniazet Z, Loridant S, Bianchi D. Acidity of SiO 2-Supported Metal Oxides in the Presence of H 2O Using the Adsorption Equilibrium Infrared Spectroscopy Method: 1. Adsorption and Coadsorption of NH 3 and H 2O on SiO 2. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:13371-13382. [PMID: 32970948 DOI: 10.1021/acs.langmuir.0c01716] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The present study is dedicated to the characterization (identification, heats of adsorption, and coverages) of the adsorbed species formed by the adsorption and coadsorption of NH3 and H2O on two SiO2 solids. Adsorption equilibrium infrared spectroscopy allowed us (a) to show that NH3 and H2O are mostly adsorbed on free SiOH groups via H bonds and (b) to determine their individual heats of adsorption: 53 and 49 kJ/mol, whatever be their coverages (Langmuir adsorption model), for NH3ads and H2Oads, respectively. These values consistent with the microcalorimetry literature data explain that their coverages are decreased upon NH3-H2O coadsorption, considering a competitive Langmuir model. However, the temperature-programmed adsorption equilibrium procedure achieved from MS data indicated that a minor amount of other NH3 species (not detected using Fourier-transform infrared) is more strongly adsorbed and that hydrolysis of SiOSi siloxane by H2O could occur in parallel. NH3-H2O coadsorption leads to the formation of NH4+ species, which involves H2O adsorbed species. Both NH3 and H2O are not adsorbed above 450 K, which means that the SiO2 contribution to the characterization of the acidity of metal oxide catalysts supported on SiO2 using NH3 as the probe molecule in the presence of H2O is negligible above this temperature.
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Affiliation(s)
- J Couble
- Université de Lyon, Université Claude Bernard Lyon 1, CNRS, IRCELYON, F-69626 Villeurbanne, France
| | - Z Buniazet
- Université de Lyon, Université Claude Bernard Lyon 1, CNRS, IRCELYON, F-69626 Villeurbanne, France
| | - S Loridant
- Université de Lyon, Université Claude Bernard Lyon 1, CNRS, IRCELYON, F-69626 Villeurbanne, France
| | - D Bianchi
- Université de Lyon, Université Claude Bernard Lyon 1, CNRS, IRCELYON, F-69626 Villeurbanne, France
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4
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Buniazet Z, Couble J, Maury S, Cabiac A, Loridant S, Bianchi D. Acidity of SiO 2-Supported Metal Oxides in the Presence of H 2O Using the AEIR Method: 2. Adsorption and Coadsorption of NH 3 and H 2O on TiO 2/SiO 2 Catalysts. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:13383-13395. [PMID: 32970949 DOI: 10.1021/acs.langmuir.0c01717] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Two different TiO2/SiO2 compounds containing TiO2 nanodomains dispersed over SiO2 were investigated applying the AEIR method at the adsorption equilibrium of NH3 and H2O from 300 to 723 K, particularly for the measurement of the individual heats of adsorption of the different species on Lewis acidic sites (LAS) and Brønsted acidic sites (BAS) as evaluation of the strength of the sites. It revealed two types of NH3 adsorption sites: the first ones could correspond either to NH3 species H-bonded to free OH groups or to coordinated weak LAS (named L1). The second ones (L2) were attributed to strongest LAS similar to those present at the surface of TiO2 nanocrystallites. They also correspond to the stronger adsorption sites of H2O. Two types of Brønsted acid sites (BAS) were additionally evidenced by the AEIR method and proposed to be specifically located on the Si-O-Ti bridging bonds at the TiO2/SiO2 interface. The heats of adsorption of the different adsorbed species provided by the AEIR method were consistent with literature data on average values of the heats of adsorption of NH3 and H2O from microcalorimetry measurements. The surface acidity of the two compounds in the presence of H2O was determined using NH3-H2O coadsorption. At T ≥ 473 K, the NH3 species on the L2 sites were not significantly displaced from the surface whatever the partial pressure of H2O studied in agreement with the Temkin competitive model using the individual heats of adsorption of the NH3 and H2O species. This model also revealed the presence of a small amount of H2O species adsorbed on L2 sites allowing H2O dissociation or/and hydrolysis of SiOTi or TiOTi bridges, leading to the formation of a much higher amount of BAS. Therefore, this original work combining the AEIR method and the Temkin competitive model provided new insights for understanding water effects on acidic oxide catalysts.
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Affiliation(s)
- Z Buniazet
- Université de Lyon, Université Claude Bernard Lyon 1, CNRS, IRCELYON, F-69626 Villeurbanne, France
| | - J Couble
- Université de Lyon, Université Claude Bernard Lyon 1, CNRS, IRCELYON, F-69626 Villeurbanne, France
| | - S Maury
- IFP Energies nouvelles, Rond-point de l'échangeur de Solaize, BP 3, F-69360 Solaize, France
| | - A Cabiac
- IFP Energies nouvelles, Rond-point de l'échangeur de Solaize, BP 3, F-69360 Solaize, France
| | - S Loridant
- Université de Lyon, Université Claude Bernard Lyon 1, CNRS, IRCELYON, F-69626 Villeurbanne, France
| | - D Bianchi
- Université de Lyon, Université Claude Bernard Lyon 1, CNRS, IRCELYON, F-69626 Villeurbanne, France
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5
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Kay Lup AN, Abnisa F, Daud WMAW, Aroua MK. Atmospheric hydrodeoxygenation of phenol as pyrolytic‐oil model compound for hydrocarbon production using Ag/TiO
2
catalyst. ASIA-PAC J CHEM ENG 2019. [DOI: 10.1002/apj.2293] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Andrew Ng Kay Lup
- Department of Chemical Engineering, Faculty of EngineeringUniversity of Malaya Kuala Lumpur Malaysia
| | - Faisal Abnisa
- Department of Chemical and Material Engineering, Faculty of EngineeringKing Abdulaziz University Jeddah Saudi Arabia
| | - Wan Mohd Ashri Wan Daud
- Department of Chemical Engineering, Faculty of EngineeringUniversity of Malaya Kuala Lumpur Malaysia
| | - Mohamed Kheireddine Aroua
- Centre for Carbon Dioxide Capture and Utilization, School of Science and TechnologySunway University Petaling Jaya Malaysia
- Department of EngineeringLancaster University Lancaster UK
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6
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A Contribution to the Experimental Microkinetic Approach of Gas/Solid Heterogeneous Catalysis: Measurement of the Individual Heats of Adsorption of Coadsorbed Species by Using the AEIR Method. Catalysts 2018. [DOI: 10.3390/catal8070265] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
The two first surface elementary steps of a gas/solid catalytic reaction are the adsorption/desorption at least one of the reactants leading to its adsorption equilibrium which can be or not disturbed by the others surface elementary steps leading to the products. The variety of the sites of a conventional catalyst may lead to the formation of different coadsorbed species such as linear, bridged and threefold coordinated species for the adsorption of CO on supported metal particles. The aim of the present article is to summarize works performed in the last twenty years for the development and applications of an analytical method named Adsorption Equilibrium InfraRed spectroscopy (AEIR) for the measurement of the individual heats of adsorption of coadsorbed species and for the validation of mathematical expressions for their adsorption coefficients and adsorption models. The method uses the evolution of the IR bands characteristic of each of coadsorbed species during the increase in the adsorption temperature in isobaric conditions. The presentation shows that the versatility of AEIR leads to net advantages as compared to others conventional methods particularly in the context of the microkinetic approach of catalytic reactions.
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7
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Couble J, Bianchi D. Experimental microkinetic approach of the CO/H2 reaction on Pt/Al2O3 using the Temkin formalism. 2. Coverages of the adsorbed CO and hydrogen species during the reaction and rate of the CH4 production. J Catal 2017. [DOI: 10.1016/j.jcat.2017.05.013] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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8
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Couble J, Bianchi D. Experimental microkinetic approach of the CO/H2 reaction on Pt/Al2O3 using the Temkin formalism. 1. Competitive chemisorption between adsorbed CO and hydrogen species in the absence of reaction. J Catal 2017. [DOI: 10.1016/j.jcat.2017.05.015] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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9
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Yakovina OA, Lisitsyn AS. Probing the H 2-Induced Restructuring of Pt Nanoclusters by H 2-TPD. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2016; 32:12013-12021. [PMID: 27779882 DOI: 10.1021/acs.langmuir.6b02847] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Metal clusters with sizes below 1 nm attract great scientific interest, but the main information on their properties still comes from quantum mechanics modeling and costly physical methods of limited availability. We have studied ultradispersed Pt/γ-Al2O3 samples with temperature-programmed desorption (TPD) and complementary adsorption/desorption techniques and observed that the H2-TPD profile of Pt/γ-Al2O3 is strongly dependent on the pretreatment conditions (0 < PH2 ≤ 1 bar; 200 K ≤ T ≤ 470 K). The results corroborate recent theoretical and spectroscopic studies predicting alterations in the structure of Pt nanoclusters under H2-treatment conditions but reveal that the restructuring needs to overcome continuous activation barriers and leads both to an increase in surface coverage and strengthening of the Pt-H bonds. This was interpreted as being a consequence of the strong interaction of Pt clusters with the support. The results extend insights into the behavior of supported metal particles and expand the potential of existing experimental techniques.
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Affiliation(s)
- Olga A Yakovina
- Boreskov Institute of Catalysis SB RAS , Novosibirsk 630090, Russian Federation
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10
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Jbir I, Couble J, Khaddar-Zine S, Ksibi Z, Meunier F, Bianchi D. Individual Heat of Adsorption of Adsorbed CO Species on Palladium and Pd–Sn Nanoparticles Supported on Al2O3 by Using Temperature-Programmed Adsorption Equilibrium Methods. ACS Catal 2016. [DOI: 10.1021/acscatal.5b02749] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Imen Jbir
- Institut
de Recherche sur la Catalyse et l’Environnement de Lyon (IRCELYON),
UMR 5256 CNRS, Université Claude Bernard Lyon I, Bat. Chevreul, 43 Boulevard du 11 Novembre 1918, 69622 Villeurbanne, France
- Laboratoire
de Chimie des Matériaux et Catalyse, Faculté des Sciences
de Tunis, Université de Tunis EL Manar, 2092 Tunis, France
| | - Julien Couble
- Institut
de Recherche sur la Catalyse et l’Environnement de Lyon (IRCELYON),
UMR 5256 CNRS, Université Claude Bernard Lyon I, Bat. Chevreul, 43 Boulevard du 11 Novembre 1918, 69622 Villeurbanne, France
| | - Sihem Khaddar-Zine
- Laboratoire
de Chimie des Matériaux et Catalyse, Faculté des Sciences
de Tunis, Université de Tunis EL Manar, 2092 Tunis, France
| | - Zouhaier Ksibi
- Laboratoire
de Chimie des Matériaux et Catalyse, Faculté des Sciences
de Tunis, Université de Tunis EL Manar, 2092 Tunis, France
| | - Fréderic Meunier
- Institut
de Recherche sur la Catalyse et l’Environnement de Lyon (IRCELYON),
UMR 5256 CNRS, Université Claude Bernard Lyon I, Bat. Chevreul, 43 Boulevard du 11 Novembre 1918, 69622 Villeurbanne, France
| | - Daniel Bianchi
- Institut
de Recherche sur la Catalyse et l’Environnement de Lyon (IRCELYON),
UMR 5256 CNRS, Université Claude Bernard Lyon I, Bat. Chevreul, 43 Boulevard du 11 Novembre 1918, 69622 Villeurbanne, France
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11
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High Selectively Catalytic Conversion of Lignin-Based Phenols into para-/m-Xylene over Pt/HZSM-5. Catalysts 2016. [DOI: 10.3390/catal6020019] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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12
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Wu HC, Chen TC, Lai NC, Yang CM, Wu JH, Chen YC, Lee JF, Chen CS. Synthesis of sub-nanosized Pt particles on mesoporous SBA-15 material and its application to the CO oxidation reaction. NANOSCALE 2015; 7:16848-16859. [PMID: 26403094 DOI: 10.1039/c5nr04943a] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
In this work, we show that the size and shape of Pt nanoparticles in SBA-15 can be controlled through vacuum and air calcination. The vacuum-calcination/H2-reduction process is used to thermally treat a 0.2 wt% Pt(4+)/SBA-15 sample to obtain small 2D clusters and single atoms that can significantly increase Pt dispersion in SBA-15. Compared with thermal treatments involving air-calcination/H2-reduction, which result in ∼4.6 nm rod-like Pt particles, vacuum-calcination/H2-reduction can dramatically reduce the size of the Pt species to approximately 0.5-0.8 nm. The Pt particles undergoing air-calcination/H2-reduction have poor conversion efficiency because the fraction of terrace sites, the major sites for CO oxidation, on the rod-like Pt particles is small. In contrast, a large amount of low-coordinated Pt sites associated with 2D Pt species and single Pt atoms in SBA-15 is effectively generated through the vacuum-calcination/H2-reduction process, which may facilitate CO adsorption and induce strong reactivity toward CO oxidation. We investigated the effect of vacuum-calcination/H2-reduction on the formation of tiny 2D clusters and single atoms by characterizing the particles, elucidating the mechanism of formation, determining the active sites for CO oxidation and measuring the heat of CO adsorption.
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Affiliation(s)
- Hung-Chi Wu
- Center for General Education, Chang Gung University, 259, Wen-Hua 1st Rd., Guishan Dist., Taoyuan City 333, Taiwan, Republic of China.
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13
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Non-Calorimetric Determination of the Adsorption Heat of Volatile Organic Compounds under Dynamic Conditions. Catalysts 2015. [DOI: 10.3390/catal5020653] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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14
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Small MW, Sanchez SI, Marinkovic NS, Frenkel AI, Nuzzo RG. Influence of adsorbates on the electronic structure, bond strain, and thermal properties of an alumina-supported Pt catalyst. ACS NANO 2012; 6:5583-5595. [PMID: 22575058 DOI: 10.1021/nn3015322] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We describe the results of an X-ray absorption spectroscopy (XAS) study of adsorbate and temperature-dependent alterations of the atomic level structure of a prototypical, noble metal hydrogenation and reforming catalyst: ∼1.0 nm Pt clusters supported on gamma alumina (Pt/γ-Al(2)O(3)). This work demonstrates that the metal-metal (M-M) bonding in these small clusters is responsive to the presence of adsorbates, exhibiting pronounced coverage-dependent strains in the clusters' M-M bonding, with concomitant modifications of their electronic structures. Hydrogen and CO adsorbates demonstrate coverage-dependent bonding that leads to relaxation of the M-M bond strains within the clusters. These influences are partially compensated, and variably mediated, by the temperature-dependent electronic perturbations that arise from cluster-support and adsorbate-support interactions. Taken together, the data reveal a strikingly fluxional system with implications for understanding the energetics of catalysis. We estimate that a 9.1 ± 1.1 kJ/mol strain exists for these clusters under H(2) and that this strain increases to 12.8 ± 1.7 kJ/mol under CO. This change in the energy of the particle is in addition to the different heats of adsorption for each gas (64 ± 3 and 126 ± 2 kJ/mol for H(2) and CO, respectively).
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Affiliation(s)
- Matthew W Small
- School of Chemical Sciences and the Fredrick Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois, USA
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15
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Gutierrez A, Kaila R, Honkela M, Slioor R, Krause A. Hydrodeoxygenation of guaiacol on noble metal catalysts. Catal Today 2009. [DOI: 10.1016/j.cattod.2008.10.037] [Citation(s) in RCA: 418] [Impact Index Per Article: 27.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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16
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Collins SE, Baltanás MA, Bonivardi AL. Heats of adsorption and activation energies of surface processes measured by infrared spectroscopy. ACTA ACUST UNITED AC 2008. [DOI: 10.1016/j.molcata.2007.08.013] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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17
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Delgado JA, Sotelo JL, Gómez JM, Gómez P. Estimation of Adsorption Parameters from Temperature-Programmed Desorption Thermograms: Application to the Adsorption of Carbon Dioxide onto Alumina. ADSORPT SCI TECHNOL 2007. [DOI: 10.1260/026361707782398146] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Affiliation(s)
- José A. Delgado
- Department of Chemical Engineering, Universidad Complutense Madrid, 28040 Madrid, Spain
| | - José L. Sotelo
- Department of Chemical Engineering, Universidad Complutense Madrid, 28040 Madrid, Spain
| | - José M. Gómez
- Department of Chemical Engineering, Universidad Complutense Madrid, 28040 Madrid, Spain
| | - Pilar Gómez
- Department of Chemical Engineering, Universidad Complutense Madrid, 28040 Madrid, Spain
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18
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Panczyk T, Gac W, Panczyk M, Borowiecki T, Rudzinski W. On the equilibrium nature of thermodesorption processes. TPD-NH3 studies of surface acidity of Ni/MgO-Al2O3 catalysts. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2006; 22:6613-21. [PMID: 16831004 DOI: 10.1021/la053191y] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
This article deals with a quantitative analysis of thermodesorption spectra of ammonia: a technique commonly applied to study the surface acidity of solids. The method used for determination of adsorption energy distributions of ammonia is the same as that published recently for the case of hydrogen thermodesorption (Panczyk, T.; et al. Langmuir 2005, 21, 7311). The developed theoretical expression describing the thermodesorption process is based on the statistical rate theory (SRT) and its analysis leads to the conclusion that majority of thermodesorption processes, carried out under flow conditions, are in fact quasi-equilibrium ones. Similar conclusion has already been drawn by some authors applying the classical absolute rate theory (ART) for analysis of thermodesorption data. This conclusion has important practical consequences. Namely, it greatly simplifies the quantitative analysis of thermodesorption processes since there is no need to use any kinetic approaches to that purpose. The quantitative analysis of thermodesorption spectra can thus be based on commonly accepted relations following from equilibrium thermodynamics. It is worth noting that in quasiequilibrium conditions either the SRT or the ART lead to this same expression with only a slightly different meaning of some constants. Thus, in quasiequilibrium conditions there is no need to decide which theoretical approach should be applied. As an illustration, the ammonia thermodesorption spectra from the modified nickel catalysts are analyzed. The catalysts were prepared by the coprecipitation method and differ by the amount of MgO and NiO, whereas the amount of Al(2)O(3) is constant and equals 30%. It was stated that the presence of MgO reduces the number of acid centers corresponding to high values of ammonia adsorption energy.
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Affiliation(s)
- Tomasz Panczyk
- Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, ul. Niezapominajek 8, 30239 Krakow, Poland.
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19
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Strunk J, Naumann d'Alnoncourt R, Bergmann M, Litvinov S, Xia X, Hinrichsen O, Muhler M. Microkinetic modeling of CO TPD spectra using coverage dependent microcalorimetric heats of adsorption. Phys Chem Chem Phys 2006; 8:1556-65. [PMID: 16633640 DOI: 10.1039/b515651c] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
CO adsorption on the ternary methanol synthesis Cu/ZnO/Al2O3 catalyst was studied in detail by means of adsorption microcalorimetry and flow temperature-programmed desorption (TPD). Based on these experimental data, we established a microkinetic analysis method, which provides information about the adsorption kinetics of CO on the catalyst surface. Experimentally derived microcalorimetric heats of adsorption were applied in a microkinetic model to simulate TPD curves with varying initial coverage. Two approaches were used: an integral approach based on evaluation of the integral heats of adsorption which predicts the experimental TPD curves roughly and provides first approximations for the preexponential factors. The second, more detailed approach was based on the simulation of the adsorption isotherm taking the experimentally determined coverage-dependence of the heat of adsorption into account. This approach led to a significantly improved agreement between experimental and simulated TPD curves. Moreover, it was possible to derive the standard entropy of adsorption. The general applicability of our approaches is demonstrated by analyzing the CO TPD and microcalorimetry data obtained with a binary ZnO-free Cu/Al2O3 catalyst.
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Affiliation(s)
- J Strunk
- Ruhr-University Bochum, Laboratory of Industrial Chemistry, D-44780, Bochum, Germany
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20
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Delgado JA, Gómez JM. Estimation of adsorption parameters from temperature-programmed-desorption thermograms: application to the adsorption of carbon dioxide onto Na- and H-mordenite. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2005; 21:9555-61. [PMID: 16207035 DOI: 10.1021/la050966u] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
In this work, a model is proposed for the estimation of the adsorption parameters from TPD thermograms when the adsorption cell can be modeled as a well-mixed reactor, evaluating the adsorption and desorption rate constants from statistical thermodynamics. The estimation procedure consists of fitting the model to the experimental TPD thermograms using numerical methods. The study of the effect of readsorption in this system reveals that this effect must be taken into account in most cases. Only with high activation energies of adsorption may this effect be negligible. The model is used to estimate the adsorption parameters of the systems CO(2)-Na-mordenite and CO(2)-H-mordenite, including an analysis about the degrees of freedom of the adsorbed phase. The estimated values of the adsorption enthalpy have been compared with the ones obtained from adsorption equilibrium data.
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Affiliation(s)
- José A Delgado
- Department of Chemical Engineering, Universidad Complutense Madrid, 28040 Madrid, Spain.
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21
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Delgado JA, Gómez JM. Modeling of temperature-programmed desorption thermograms for the determination of adsorption heat considering pore and surface diffusion. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2005; 21:3503-3510. [PMID: 15807595 DOI: 10.1021/la0471238] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
In this work, two partial differential equation-based models have been proposed for the quantitative analysis of temperature-programmed desorption (TPD) thermograms when the adsorption cell can be modeled as a well-mixed reactor, using the Langmuir equation as the adsorption isotherm and including the effect of diffusional resistance. One model considers pore diffusion, and the other considers surface diffusion. For both models, the rate of adsorption is proportional to the gas pressure. By nondimensionalizing these models, the range of design parameters for which the accumulation in the gas cell, diffusional resistance, and readsorption have an important effect on the TPD signal is proposed. An important conclusion is that the dimensionless numbers accounting for the diffusional resistance and the corresponding range of parameters are quite different for both mechanisms. The models have been validated with two systems where surface and pore diffusion are the relevant mechanisms: (i) CO2-Na-mordenite and (ii) CO2-Na-mordenite pellets.
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Affiliation(s)
- José A Delgado
- Department of Chemical Engineering, Universidad Complutense Madrid, 28040 Madrid, Spain.
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22
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Collins SE, Baltanás MA, Bonivardi AL. Hydrogen chemisorption on gallium oxide polymorphs. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2005; 21:962-970. [PMID: 15667175 DOI: 10.1021/la0481389] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The chemisorption of H(2) over a set of gallia polymorphs (alpha-, beta-, and gamma-Ga(2)O(3)) has been studied by temperature-programmed adsorption equilibrium and desorption (TPA and TPD, respectively) experiments, using in situ transmission infrared spectroscopy. Upon heating the gallium oxides above 500 K in 101.3 kPa of H(2), two overlapped infrared signals developed. The 2003- and 1980-cm(-1) bands were assigned to the stretching frequencies of H bonded to coordinatively unsaturated (cus) gallium cations in tetrahedral and octahedral positions [nu(Ga(t)-H) and nu(Ga(o)-H), respectively]. Irrespective to the gallium cation geometrical environment, (i) a linear relationship between the integrated intensity of the whole nu(Ga-H) infrared band versus the Brunauer-Emmett-Teller surface area of the gallia was found and (ii) TPA and TPD results revealed that molecular hydrogen is dissociatively chemisorbed on any bulk gallium oxide polymorph following two reaction pathways. An endothermal, homolytic dissociation occurs over surface cus-gallium sites at T > 450 K, giving rise to Ga-H(I) bonds. The heat and entropy of this type I hydrogen adsorption were determined by the Langmuir's adsorption model as Deltah(I) = 155 +/- 25 kJ mol(-1) and Deltas(I) = 0.27 +/- 0.11 kJ mol(-1) K(-1). In addition, another exothermic, heterolytic adsorption sets in already in the low-temperature region. This type of hydrogen chemisorption involves surface Ga-O-Ga species, originating GaO-H and Ga-H(II) bonds which can only be removed from the gallia surface after heating under evacuation at T > 650 K. The measured desorption energy of this last, second-order process was equal to 77 +/- 10 kJ mol(-1). The potential of the H(2) chemisorption as a tool to measure or estimate the specific surface area of gallia and to discern the nature and proportion of gallium cation coordination sites on the surface of bulk gallium oxides is also analyzed.
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Affiliation(s)
- Sebastián E Collins
- Instituto de Desarrollo Tecnológico para la Industria Química (CONICET, UNL) Güemes 3450, S3000GLN Santa Fe, Argentina
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Derrouiche S, Gravejat P, Bianchi D. Heats of Adsorption of Linear CO Species Adsorbed on the Au° and Ti+δ Sites of a 1% Au/TiO2 Catalyst Using in Situ FTIR Spectroscopy under Adsorption Equilibrium. J Am Chem Soc 2004; 126:13010-5. [PMID: 15469299 DOI: 10.1021/ja0470719] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The heats of adsorption of two linear CO species adsorbed on the Au degrees particles (denoted L(Au degrees)) and on the Ti(+delta) sites (denoted L(Ti+delta)) of a 1% Au/TiO(2) catalyst are determined as the function of their respective coverage by using the AEIR procedure (adsorption equilibrium infrared spectroscopy) previously developed. Mainly, the evolutions of the IR band area of each adsorbed species (2184 cm(-1) for L(Ti+delta) and at 2110 cm(-1) for L(Au degrees)) as a function of the adsorption temperature T(a), at a constant CO adsorption pressure P(CO), provide the evolutions of the coverages theta(LTi+delta) and theta(LAu degrees ) of each adsorbed CO species with T(a) in isobar conditions that give the individual heats of adsorption. It is shown that they linearly vary from 74 to 47 kJ/mol for L(Au degrees ) and from 50 to 40 kJ/mol for L(Ti+delta) at coverages 0 and 1, respectively. These values are consistent with literature data on model Au particles and TiO(2). In particular, it is shown that the mathematical formalism supporting the AEIR procedure can be applied to literature data on Au-containing solids (single crystals and model particles).
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Affiliation(s)
- Salim Derrouiche
- Contribution from the Laboratoire d'Application de la Chimie à l'Environnement (LACE), UMR 5634, Université Claude Bernard, Lyon-I, Batiment 303, 43 Boulevard du 11 Novembre 1918, 69622 Villeurbanne, France
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