Temporal Analysis of Products (TAP)—A Unique Catalyst Evaluation System with Submillisecond Time Resolution

Gleaves, John; Ebner, J. R.; Kuechler, T. C.

doi:10.1080/01614948808078616

Cited by 422 publications

(216 citation statements)

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“…This broadening effect gave an overlap between desorption temperatures in the LT and MT sites of ZSM-5 catalyst during methanol and DME desorption allowing for their direct comparison. In the TAP reactor, it has been shown that such re-adsorption can hardly be neglected over porous catalysts [42]. The higher activation energies of desorption obtained using the detailed elementary step model is due to re-adsorption effects which the Redhead method failed to account for.…”

Section: Comparing Redhead Methods To the Detailed Elementary Step Modelmentioning

confidence: 99%

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Mechanistic Insights into the Desorption of Methanol and Dimethyl Ether Over ZSM-5 Catalysts

et al. 2017

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The desorption of methanol and dimethyl ether has been studied over fresh and hydrocarbon-occluded ZSM-5 catalysts with Si/Al ratios of 25, 36 and 135 using a temporal analysis of products reactor. The catalysts were characterized by XRD, SEM, N 2 physisorption and pyridine FT-IR. The crystal size increases with Si/Al ratio from 0.10 to 0.78 µm. The kinetic parameters were obtained using the Redhead method and a plug flow reactor model with coupled convection, adsorption and desorption steps. ZSM-5 catalysts with Si/Al ratios of 25 and 36 exhibit three adsorption sites (low, medium, and high temperature sites), while there is no difference between medium and high temperature sites at a Si/Al ratio of 135. Molecular adsorption on the low temperature site and dissociative adsorption on the medium and high temperature sites give a good match between experiment and the plug flow reactor model. The DME desorption activation energy was systematically higher than that of methanol. Adsorption stoichiometry shows that methanol and DME form clusters onto the binding sites. When non-activated re-adsorption is accounted for, a local equilibrium is reached only on the low and medium temperature binding sites. No differences were observed, other than in site densities, when extracting the kinetic parameters for fresh and activated ZSM-5 catalysts at full coverage. Graphical AbstractElectronic supplementary material The online version of this article (https://doi

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Section: Comparing Redhead Methods To the Detailed Elementary Step Modelmentioning

confidence: 99%

“…The TAP reactor developed by Gleaves and co-workers [42] is conventionally used for pulse response experiments due to its sub-millisecond time resolution. Here, it has been exploited for TPD experiments as its operation under vacuum is necessary to reduce the influence of re-adsorption.…”

Section: Limiting Factorsmentioning

confidence: 99%

Mechanistic Insights into the Desorption of Methanol and Dimethyl Ether Over ZSM-5 Catalysts

et al. 2017

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“…TAP (temporal analysis of products) reactor experiments 36 showed that with a sufficient dose of oxygen on the VOPO surface prior to exposure to n-butane, subsequent exposure to butane leads to selectively fully oxidized maleic anhydride, without intermediates being released. This shows that the reaction is localized and that all seven oxygen required for completing the reaction are somehow stored near the surface and are accessible to the substrate.…”

Section: Implication For the Catalytic Reactionmentioning

confidence: 99%

The magnetic and electronic structure of vanadyl pyrophosphate from density functional theory

Cheng

Nielsen

Tahir-Kheli

et al. 2011

Phys. Chem. Chem. Phys.

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We have studied the magnetic structure of the high symmetry vanadyl pyrophosphate ((VO) 2 P 2 O 7 , VOPO), focusing on the spin exchange couplings, using density functional theory (B3LYP) with the full three-dimensional periodicity. VOPO involves four distinct spin couplings: two larger couplings exist along the chain direction (a-axis), which we predict to be antiferromagnetic, J OPO = À156.8 K and J O = À68.6 K, and two weaker couplings appear along the c (between two layers) and b directions (between two chains in the same layer), which we calculate to be ferromagnetic, J layer = 19.2 K and J chain = 2.8 K. Based on the local density of states and the response of spin couplings to varying the cell parameter a, we found that J OPO originates from a super-exchange interaction through the bridging -O-P-O-unit. In contrast, J O results from a direct overlap of 3d x 2 À y 2 orbitals on two vanadium atoms in the same V 2 O 8 motif, making it very sensitive to structural fluctuations. Based on the variations in V-O bond length as a function of strain along a, we found that the V-O bonds of V-(OPO) 2 -V are covalent and rigid, whereas the bonds of V-(O) 2 -V are fragile and dative. These distinctions suggest that compression along the a-axis would have a dramatic impact on J O , changing the magnetic structure and spin gap of VOPO. This result also suggests that assuming J O to be a constant over the range of 2-300 K whilst fitting couplings to the experimental magnetic susceptibility is an invalid method. Regarding its role as a catalyst, the bonding pattern suggests that O 2 can penetrate beyond the top layers of the VOPO surface, converting multiple V atoms from the +4 to +5 oxidation state, which seems crucial to explain the deep oxidation of n-butane to maleic anhydride.

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“…The Temporal Analysis of Products (TAP) [54] technique is the main tool to study the reaction mechansim of the Di-Air system. Therefore, Chapter 2 describes the dedicated home-made instrument for this technique.…”

Section: Outline Of the Thesismentioning

confidence: 99%

Next Generation Automotive DeNO_x Catalysts: Ceria What Else?

et al. 2015

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Temporal analysis of products (TAP) was used to study NO reduction to N2 over H2 and C3H6‐reduced La‐Zr doped ceria at 560 °C. (La‐Zr doped) ceria is found to be capable of fuel oxidation and NO reduction. NO dissociates on oxygen anion defects, thereby refilling these vacancies with oxygen anions and forming N2. The carbonaceous deposits, in case the catalyst was reduced by C3H6, are oxidized by oxygen species originating from lattice oxygen. This recreates oxygen anion defects, which enables substantial additional NO reduction. These findings may open a new perspective on the understanding of DeNOx by hydrocarbons.

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Temporal Analysis of Products (TAP)—A Unique Catalyst Evaluation System with Submillisecond Time Resolution

Cited by 422 publications

References 46 publications

Mechanistic Insights into the Desorption of Methanol and Dimethyl Ether Over ZSM-5 Catalysts

Mechanistic Insights into the Desorption of Methanol and Dimethyl Ether Over ZSM-5 Catalysts

The magnetic and electronic structure of vanadyl pyrophosphate from density functional theory

Next Generation Automotive DeNO_x Catalysts: Ceria What Else?

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Temporal Analysis of Products (TAP)—A Unique Catalyst Evaluation System with Submillisecond Time Resolution

Cited by 422 publications

References 46 publications

Mechanistic Insights into the Desorption of Methanol and Dimethyl Ether Over ZSM-5 Catalysts

Mechanistic Insights into the Desorption of Methanol and Dimethyl Ether Over ZSM-5 Catalysts

The magnetic and electronic structure of vanadyl pyrophosphate from density functional theory

Next Generation Automotive DeNOx Catalysts: Ceria What Else?

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Product

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Next Generation Automotive DeNO_x Catalysts: Ceria What Else?