Spatial distributions of desorption flow as an indicator for a precursor state in several systems

Kislyuk, M. U.; Savkin, V. V.; Tretyakov, Ian

doi:10.1007/bf02756144

Cited by 10 publications

(13 citation statements)

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“…Furthermore, the TPD curve for the V(benzene) 2 /C 18 -SAM substrate exhibits a sharp decrease after the peak maximum. In general, a peak profile of a TPD spectrum reflects the reaction order of a desorption process. , Thus, the peak shape difference observed herein suggests that the desorption process of the V(benzene) 2 clusters is significantly different between the gold and the C 18 -SAM substrates. In addition, the integrated areas of the V(benzene) 2 TPD spectra, corresponding to the amount of V(benzene) 2 clusters deposited intact, are much larger for the C 18 -SAM than for the gold substrate.…”

Section: Results and Analysismentioning

confidence: 78%

Room-Temperature Isolation of V(benzene)₂ Sandwich Clusters via Soft-Landing into n-Alkanethiol Self-Assembled Monolayers

et al. 2006

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The adsorption state and thermal stability of V(benzene)2 sandwich clusters soft-landed onto a self-assembled monolayer of different chain-length n-alkanethiols (Cn-SAM, n = 8, 12, 16, 18, and 22) were studied by means of infrared reflection absorption spectroscopy (IRAS) and temperature-programmed desorption (TPD). The IRAS measurement confirmed that V(benzene)2 clusters are molecularly adsorbed and maintain a sandwich structure on all of the SAM substrates. In addition, the clusters supported on the SAM substrates are oriented with their molecular axes tilted 70-80 degrees off the surface normal. An Arrhenius analysis of the TPD spectra reveals that the activation energy for the desorption of the supported clusters increases linearly with the chain length of the SAMs. For the longest chain C22-SAM, the activation energy reaches approximately 150 kJ/mol, and the thermal desorption of the supported clusters can be considerably suppressed near room temperature. The clear chain-length-dependent thermal stability of the supported clusters observed here can be explained well in terms of the cluster penetration into the SAM matrixes.

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Section: Results and Analysismentioning

confidence: 78%

Room-Temperature Isolation of V(benzene)₂ Sandwich Clusters via Soft-Landing into n-Alkanethiol Self-Assembled Monolayers

et al. 2006

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“…The peak maxima (i.e., “peak” temperatures) in the desorption spectra shifted to lower temperatures with increasing fluence, and there was an increased degree of tailing on the high-temperature side of the desorption spectra, increasing with fluence. As discussed before, tailing on the high-temperature side of a desorption spectrum indicates that there might have been diffusion of the alcohols into the monolayer after dosing and before TPD . For low butanol fluence, the desorption spectra are more symmetric, suggesting an apparent-second- order desorption process, and slightly more broad compared to the desorption spectra for high butanol fluence.…”

Section: Resultsmentioning

confidence: 77%

“…The peak shape for 1-butanol (and the other low-molecular-weight alcohols) desorption from the hydroxyl-terminated surface thus exhibits a second-order-like desorption peak shape at the lowest fluence studied, although it would be difficult to imagine a physical scenario where this would be the case. Although there are several factors that influence the peak shape of a TPD spectrum, evidence for diffusion in the monolayer is illustrated by the long tails in the desorption spectra on the high-temperature side of the peaks . The leading edges of the desorption spectra shifted to lower temperatures as the fluence was increased.…”

Section: Resultsmentioning

confidence: 99%

“…In the special case where the desorption energy is not dependent on coverage, the desorption energy is directly related to the temperature at the peak maximum in a TPD spectrum, i.e., E d ≈ 25 RT max , where T max is the peak temperature . Under these circumstances the trend of the desorption energies as a function of coverage would, of course, follow the trend of the shift in temperatures at the peak maxima.…”

Section: Resultsmentioning

confidence: 99%

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Interactions of Alcohols with Hydroxyl- and Methyl-Terminated Self-Assembled Monolayer Surfaces Studied by Temperature-Programmed Desorption

Vogt

Beebe

1999

J. Phys. Chem. B

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The interactions of low-molecular-weight n-alcohols (n-C x H 2x+1 OH for x ) 1-6) with 11-mercaptoundecanol (HO(CH 2 ) 11 SH) or octadecyl mercaptan (CH 3 (CH 2 ) 17 SH) adsorbed onto a nickel(111) single-crystal surface were studied by temperature-programmed desorption (TPD). Angle-dependent X-ray photoelectron spectroscopy (ADXPS) was used to characterize the adsorption of HO(CH 2 ) 11 SH and CH 3 (CH 2 ) 17 SH molecules to determine their arrangements on the nickel(111) surface. The TPD spectra for the desorption of alcohols from the hydroxylterminated and the methyl-terminated self-assembled monolayer surfaces at various alcohol fluences were analyzed by the threshold TPD method (TTPD) to determine their desorption energies as a function of the alcohol fluence. The TTPD-calculated alcohol desorption energies from the hydroxyl-terminated surface increased from 10 to 20 kJ mol -1 for the lowest fluences to 40-60 kJ mol -1 for the highest fluences; from the methyl-terminated surface the desorption energy increased from 10 to 25 kJ mol -1 for the lowest fluences to 45-55 kJ mol -1 for the highest fluences.

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“…Kislyuk 15 investigou, através de simulações, o efeito das interações laterais entre as espécies adsorvidas no catalisador e concluiu que este efeito aumenta a energia de ativação estimada experimentalmente. Tonge 16 estudou a influência da distribuição de diâmetros de partícula da amostra e sugeriu que a faixa de diâ-metro de partícula deve ser o mais estreita possível para prevenir o aparecimento de artefatos no perfil de redução.…”

Section: Introductionunclassified

Análise estatística e optimização de perfis de redução termoprogramada (TPR)

Nele¹,

Moreno²,

Andrade³

2006

Quím. Nova

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Recebido em 11/2/05; aceito em 14/10/05; publicado na web em 14/3/06 STATISTICAL ANALYSIS AND OPTIMIZATION OF TEMPERATURE PROGRAMMED REDUCTION (TPR) ANALYSIS. The effect of operational variables and their interaction in TPR profiles was studied using a fractional factorial experimental design. The heating rate and the reducing agent concentration were found to be the most important variables determining the resolution and sensitivity of the technique. They showed opposite effects. Therefore, they should be manipulated preferentially in order to obtain optimized TPR profiles. The effect of sample particle size was also investigated. The tests were carried out within a Cu/Zn/ Al 2 O 3 catalyst used for the water-gas shift reaction that presented two distinct species of Cu 2+ in TPR profiles.Keywords: TPR; temperature programmed reduction; experimental design. INTRODUÇÃOA redução termoprogramada (TPR) é uma técnica de caracterização de materiais que faz parte do conjunto de técnicas conhecidas como termoanalíticas. O perfil de TPR é capaz de fornecer uma impressão digital do material analisado e prover informações sobre a estrutura interna e superficial, a um baixo custo operacional e de montagem do equipamento 1 . Para catálise heterogênea esta técnica apresenta as vantagens adicionais de permitir o estudo da superfície do catalisador em condições próximas às reacionais, sem necessidade de vácuo.A idéia básica da técnica, pioneiramente utilizada por Robertson 2 em um equipamento similar ao desenvolvido por Cvetanovic 3 para estudos de TPD (dessorção termoprogramada), consiste em monitorar a redução de uma amostra sob fluxo de gás redutor (usualmente H 2 ou CO) diluído em gás inerte (N 2 ou Ar), enquanto a temperatura é aumentada linearmente com o tempo. A técnica é altamente sensível à presença de espécies redutíveis e tem sido muito utilizada na caracterização de catalisadores mássicos e suportados, especialmente em problemas como estudo da redução de íons em zeólitas 4 , influência de diferentes suportes em um sistema catalítico (SMSI -"Strong Metal-Support Interaction") [5][6][7] , influência das condições dos pré-tratamentos nas propriedades dos catalisadores 6,8 , efeito dos íons dos metais de transição na redutibilidade de óxidos metálicos 9 , investigação de formação de ligas em catalisadores multimetálicos e o estado do metal no catalisador 1 . Apesar da grande importância da interpretação dos perfis de redução em relação às variáveis operacionais (concentração de agente redutor, vazão de gás, taxa de aquecimento e quantidade de amostra), poucos são os trabalhos na literatura que lidam com a influên-cia das condições experimentais nos perfis de redução 10 . Bosh 11 pesquisou a influência das variáveis operacionais nos perfis de redução do V 2 O 5 e Monti 12 analisou a influência dessas variáveis operacionais sobre a temperatura de máximo consumo de H 2 (Tm) na redução do NiO. Esses autores observaram tendên-cias nos efeitos das variáveis operacionais, como o aumento da temperatura de máxima redução com o a...

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Spatial distributions of desorption flow as an indicator for a precursor state in several systems

Cited by 10 publications

References 5 publications

Room-Temperature Isolation of V(benzene)₂ Sandwich Clusters via Soft-Landing into n-Alkanethiol Self-Assembled Monolayers

Room-Temperature Isolation of V(benzene)₂ Sandwich Clusters via Soft-Landing into n-Alkanethiol Self-Assembled Monolayers

Interactions of Alcohols with Hydroxyl- and Methyl-Terminated Self-Assembled Monolayer Surfaces Studied by Temperature-Programmed Desorption

Análise estatística e optimização de perfis de redução termoprogramada (TPR)

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Spatial distributions of desorption flow as an indicator for a precursor state in several systems

Cited by 10 publications

References 5 publications

Room-Temperature Isolation of V(benzene)2 Sandwich Clusters via Soft-Landing into n-Alkanethiol Self-Assembled Monolayers

Room-Temperature Isolation of V(benzene)2 Sandwich Clusters via Soft-Landing into n-Alkanethiol Self-Assembled Monolayers

Interactions of Alcohols with Hydroxyl- and Methyl-Terminated Self-Assembled Monolayer Surfaces Studied by Temperature-Programmed Desorption

Análise estatística e optimização de perfis de redução termoprogramada (TPR)

Contact Info

Product

Resources

About

Room-Temperature Isolation of V(benzene)₂ Sandwich Clusters via Soft-Landing into n-Alkanethiol Self-Assembled Monolayers

Room-Temperature Isolation of V(benzene)₂ Sandwich Clusters via Soft-Landing into n-Alkanethiol Self-Assembled Monolayers