Thin-Zone TAP Reactor versus Differential PFR:  Analysis of Concentration Nonuniformity for Gas−Solid Systems

Shekhtman, Sergiy O.; Yablonsky, Gregory S.

doi:10.1021/ie050554g

Cited by 50 publications

(33 citation statements)

References 13 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…One of the main advantages of the TAP experiment is the ability to characterize kinetics at high conversion while maintaining uniformity in both the catalyst bed and gas phase composition. In previous work, the upper limit for conversion in the thin zone TAP reactor was described as 80% (where nonuniformity would not exceed 20%) based on a linear analytical estimate [30]. Our conversion measurements for the cobalt samples in this work exceed this guideline so the reliability of the data may be questioned.…”

Section: Ammonia Conversionmentioning

confidence: 66%

“…Our conversion measurements for the cobalt samples in this work exceed this guideline so the reliability of the data may be questioned. The topic of non-uniformity has been previously addressed in great detail theoretically [30,31]. Figure 4A from Shekhtman et al [30] compares non-uniformity as a function of conversion.…”

Section: Ammonia Conversionmentioning

confidence: 99%

“…The topic of non-uniformity has been previously addressed in great detail theoretically [30,31]. Figure 4A from Shekhtman et al [30] compares non-uniformity as a function of conversion. For the thin-zone TAP reactor, they provide the calculation of non-uniformity according to:…”

Section: Ammonia Conversionmentioning

confidence: 99%

See 2 more Smart Citations

Transient Kinetic Experiments within the High Conversion Domain: The Case of Ammonia Decomposition

et al. 2019

View full text Add to dashboard Cite

In the development of catalytic materials, a set of standard conditions is needed where the kinetic performance of many samples can be compared. This can be challenging when a sample set covers a broad range of activity. Precise kinetic characterization requires uniformity in the gas and catalyst bed composition. This limits the range of convecting devices to low conversion (generally <20%). While steady-state kinetics offer a snapshot of conversion, yield and apparent rates of the slow reaction steps, transient techniques offer much greater detail of rate processes and hence more information as to why certain catalyst compositions offer better performance. In this work, transient experiments in two transport regimes are compared: an advecting differential plug flow reactor (PFR) and a pure-diffusion temporal analysis of products (TAP) reactor. The decomposition of ammonia was used as a model reaction to test three simple materials: polycrystalline iron, cobalt and a bimetallic preparation of the two. These materials presented a wide range of activity and it was not possible to capture transient information in the advecting device for all samples at the same conditions while ensuring uniformity. We push the boundary for the theoretical estimates of uniformity in the TAP device and find reliable kinetic measurement up to 90% conversion. However, what is more advantageous from this technique is the ability to observe the time-dependence of the reaction rate rather than just singular points of conversion and yield. For example, on the iron sample we observed reversible adsorption of ammonia and on cobalt materials we identify two routes for hydrogen production. From the time-dependence of reactants and product, the dynamic accumulation was calculated. This was used to understand the atomic distribution of H and N species regulated by the surface of different materials. When ammonia was pulsed at 550 °C, the surface hydrogen/nitrogen, (H/N), ratios that evolved for Fe, CoFe and Co were 2.4, 0.25 and 0.3 respectively. This indicates that iron will store a mixture of hydrogenated species while materials with cobalt will predominantly store NH and N. While much is already known about iron, cobalt and ammonia decomposition, the goal of this work was to demonstrate new tools for comparing materials over a wider window of conversion and with much greater kinetic detail. As such, this provides an approach for detailed kinetic discrimination of more complex industrial samples beyond conversion and yield.

show abstract

Section: Ammonia Conversionmentioning

confidence: 66%

Section: Ammonia Conversionmentioning

confidence: 99%

See 1 more Smart Citation

Transient Kinetic Experiments within the High Conversion Domain: The Case of Ammonia Decomposition

et al. 2019

View full text Add to dashboard Cite

show abstract

“…Recently, a detailed estimation of the validity of TZTR-model was reported. 139 There are a number of approaches/methodologies in the TAP data analysis which are discussed in detail in the literature, including the moment-based integral approach, 19,106,140,141 differential approach, 142 curve fitting, 31,108,123,124,127,[143][144][145][146][147][148][149] as well as the extraction of kinetic parameters. 19,106 Briefly, the moment-based theory 106 is an integral analysis of each individual pulse in the series of pulses, both reactants and products.…”

Section: Discussionmentioning

confidence: 99%

Forty years of temporal analysis of products

Morgan

Maguire

Fushimi

et al. 2017

Catal. Sci. Technol.

131

101

View full text Add to dashboard Cite

A detailed understanding of reaction mechanisms and kinetics is required in order to develop and optimize catalysts and catalytic processes. While steady-state investigations are known to give a global view of the catalytic system, transient studies are invaluable since they can provide more comprehensive insight into elementary steps. For almost forty years temporal analysis of products (TAP) has been successfully utilized for transient studies of gas phase heterogeneous reactions, and there have been a number of advances in instrumentation and numerical modeling methods in that time. Since TAP is a complex methodology it is often viewed as a niche specialty. With the purpose to make TAP more relevant and approachable to a wider segment of the catalytic research community, part of the intention of this work is to highlight the significant contributions TAP has made to elucidating mechanistic and kinetic aspects of complex, multistep heterogeneous reactions. With this in mind, an outlook is also disclosed for the technique in terms of what is needed to revitalize the field and make it more applicable to the recent advances in catalyst characterization (e.g. operando modes).

show abstract

“…Catalyst particles are usually sandwiched between two inert zones of quartz particles, in a ''thin-zone'' configuration (Fig. 5) [31][32][33][34]. The thickness of the catalyst zone is made very small compared to the length of the reactor, so that the change of concentration in the catalyst zone is small, and the relative concentration gradient in the catalyst zone becomes insignificant.…”

Section: Kinetic Characterizationmentioning

confidence: 99%

Techniques for Fabricating Nanoscale Catalytic Circuits

et al. 2008

Self Cite

View full text Add to dashboard Cite

This paper describes the development of a new technique, atomic beam deposition (ABD), for the fabrication of catalysts with different active sites capable of catalyzing different chemical reactions. Using ABD, submonolayer amounts of Te and Cu atoms were deposited on vanadyl pyrophosphate (VPO) catalyst particles, and precise non-steady-state kinetic characterization was performed using the temporal analysis of products (TAP) reactor immediately following deposition. Results from TAP Knudsen pulse response experiments determine if small changes in the metal surface composition would produce detectable changes in catalytic properties. Partial oxidation of 1-butene to furan was used as the test reaction. Furthermore, this paper also demonstrates the sensitivity of the TAP reactor by measuring oxygen uptake on a single 350 lm diameter polycrystalline Pt particle packed in a bed with 100,000 inert quartz particles of similar dimensions. The Pt experiments demonstrate the precise manipulation of surface oxygen content.

show abstract

Thin-Zone TAP Reactor versus Differential PFR: Analysis of Concentration Nonuniformity for Gas−Solid Systems

Cited by 50 publications

References 13 publications

Transient Kinetic Experiments within the High Conversion Domain: The Case of Ammonia Decomposition

Transient Kinetic Experiments within the High Conversion Domain: The Case of Ammonia Decomposition

Forty years of temporal analysis of products

Techniques for Fabricating Nanoscale Catalytic Circuits

Contact Info

Product

Resources

About