Thin layer of carbon-nano-fibers (CNFs) as catalyst support for fast mass transfer in hydrogenation of nitrite

Chinthaginjala, J.K.; Bitter, Johannes H.; Lefferts, Leon

doi:10.1016/j.apcata.2010.05.013

Cited by 58 publications

(72 citation statements)

References 53 publications

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“…Calculation of TOF based on the CO chemisorption data, despite the limited accuracy, results in very similar numbers (0.15 ± 0.05 s -1 ) for 2.6 nm and 30 nm particles which also suggests that the actual TOF remains constant with changing particle size. In our previous work [9,13] TOFs of 0.021s -1 (based on CO chemisorption) were reported for hairy foam supported Pd particles of varying dispersion from 5 to 10 %. These catalysts were prepared without PVA, thus having much a much broader size distribution, and no PVA coordinating to the palladium surface.…”

Section: Discussionmentioning

confidence: 99%

“…It is known that nitrite ions are converted to ammonium and nitrogen exclusively under the conditions used in this study [9,13] the yield of nitrogen was therefore calculated from the difference between the nitrite conversion and the ammonium yield.…”

Section: Catalytic Hydrogenation Of Nitritementioning

confidence: 99%

“…Hairy foams were prepared by growing CNFs on Ni foam at 440°C by using 25% ethylene in nitrogen as described in detail previously [9] and the CNFs were not further pre-treated.…”

Section: Cnf-ni Foam Preparationmentioning

confidence: 99%

“…It is well known that nitrite reduction is an extremely fast reaction, so that concentration gradients in the internal of catalyst particles or catalyst layers can easily occur, influencing reaction rates and selectivity. Our previous work [9] demonstrated that catalysts supported on thin macroporous layers of entangled Carbon-Nano-Fibers (CNF) provide efficient mass transfer, thus resulting in intrinsic rates and selectivity. Further, for Pd-CNF catalysts with large Pd particles (Pd dispersion 5 -10%) the nitrite turn-overfrequency (TOF) was found to be constant within the experimental error, which can be explained by the large Pd particle size.…”

Section: Introductionmentioning

confidence: 99%

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Nitrite reduction over Pd supported CNFs: Metal particle size effect on selectivity

et al. 2012

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Pd catalysts supported on carbon-nano-fibres (CNFs) were synthesized via Pd colloids stabilized with polyvinyl-alcohol (PVA). Pd catalysts with narrow particle sizes distributions and mean Pd sizes between 2.6 and 30nm were immobilized on CNFs. Characterization with COchemisorption and transmission electron microscopy (TEM) revealed that a significant part of the Pd surface is blocked by the polymer layer on the Pd particles. The prepared catalysts were tested for nitrite reduction in water, resulting in formation of nitrogen and ammonia. Turn over frequencies were found to be independent of Pd particle size while selectivity to ammonia clearly decreased with increasing Pd particle size.

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Section: Discussionmentioning

confidence: 99%

Section: Catalytic Hydrogenation Of Nitritementioning

confidence: 99%

“…Hairy foams were prepared by growing CNFs on Ni foam at 440°C by using 25% ethylene in nitrogen as described in detail previously [9] and the CNFs were not further pre-treated.…”

Section: Cnf-ni Foam Preparationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Nitrite reduction over Pd supported CNFs: Metal particle size effect on selectivity

et al. 2012

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“…Furthermore, conventional methods concentrate removed contaminates in a secondary waste streams, which requires further treatment [97].…”

Section: Nitrite and Bromate Removal From Aqueous Solutionsmentioning

confidence: 99%

Catalytic microreactors for aqeous phase reactions : carboon nano fibers as catalyst support

Thakur

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This thesis describes various aspects of the development of carbon nanofiber supported catalyst layers on structured internals of microreactors made from silicon technology based materials (e.g. fused silica and/or silicon). These microreactors are intended to be used for heterogeneously catalyzed liquid phase reactions, in this case for aqueous phase removal of nitrite and bromate to evaluate the performance of such systems and demonstrate their benefit over conventional catalyst support material.The synthesis of stable carbon nanofiber layer on flat substrates (representing surfaces of microreactor channel walls) is a requisite for obtaining the know-how to translate it for preparing these layers inside microreactor channels. Chapter 2 is a detailed study of CNF synthesis using thin metal film configurations with nickel (Ni) as growth catalyst and different metals (i.e. Ti, Ti-W and Ta) as adhesion layer between nickel and fused silica substrates. Although CNFs could be synthesized on 25 nm nickel with a titanium adhesion layer (10-200 nm), titanium is not a good adhesion material.The use of a 10 nm thick adhesion layer of titanium-tungsten or tantalum resulted in the formation of well-attached CNF-layers. The carbon nanofibers in these layers were entangled, quasi-crystalline and showed tip-type growth mode. Although for both metal layer configurations, i.e. Ni/Ti-W and Ni/Ta, the thickness of the CNF layer was similar under the same growth conditions, the diameter of the fibers was smaller in case of Ni/Ta (20-50 nm) compared to Ni/Ti-W (80-125 nm). This is found to be related to the grain size of the nickel nanoparticles formed during the reduction treatment prior to the CNF synthesis step. ii || SummaryThe work presented in chapter 3 describes essential understanding about tuning and/or optimization of the overall CNF layer morphology, by evaluating the influence of various growth parameters during catalytic thermal chemical vapour deposition of Ni/Ti-W and Ni/Ta on fused silica and oxidized silicon substrates. It was found that the most important parameters were ethylene concentration and addition of hydrogen to the reactant mixture. Open, structured CNF layers with entangled morphology were formed for ethylene concentrations ≥ 25 vol.%. Moreover, addition of hydrogen to ethylene significantly enhanced the rate of formation of CNFs, and at the same time In chapter 4 the preparation and characterization of a CNF supported catalyst layer on flat surfaces and inside microchannels has been shown. Ruthenium catalytic nanoparticles on carbon nanofiber support layers were realized via homogeneous deposition precipitation and pulsed laser deposition. CNF layers are functionalized by oxidation with nitric acid to facilitate Ru deposition. Besides removal of exposed nickel (used for CNF-growth), an acid treatment forms oxygen-containing groups on the surfaces of CNFs (mainly carboxyl and hydroxyl groups). Ruthenium was anchored on oxidized CNF layers by means of HPD and PLD. Critical issues for a good dispersion of...

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Carbon Nanotubes: A Promising Catalyst Support Material for Supercritical Water Gasification of Biomass Waste

Vlieger¹,

Thakur²,

Lefferts³

et al. 2012

ChemCatChem

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Supercritical water (SCW) as a reaction medium is especially promising for the production of renewable chemicals from biomass. Stability issues of catalyst support materials in SCW are a major setback for these reactions and hinder the further development and industrial exploitation of this technique. The development of stable catalytic support materials for reactions in SCW is, therefore, of great importance. Carbon nanotubes (CNTs) are widely recognized for their significant physical and chemical stability, high heat conductivity, and open structure. These properties have already been explored for different applications. We show that CNTs are a promising stable catalyst support material for reactions in SCW. As an illustration of the applicability of CNTs in SCW, we demonstrate the efficiency of Pt‐CNTs as catalysts for the production of hydrogen by reforming of ethylene glycol and acetic acid in SCW.

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Thin layer of carbon-nano-fibers (CNFs) as catalyst support for fast mass transfer in hydrogenation of nitrite

Cited by 58 publications

References 53 publications

Nitrite reduction over Pd supported CNFs: Metal particle size effect on selectivity

Nitrite reduction over Pd supported CNFs: Metal particle size effect on selectivity

Catalytic microreactors for aqeous phase reactions : carboon nano fibers as catalyst support

Carbon Nanotubes: A Promising Catalyst Support Material for Supercritical Water Gasification of Biomass Waste

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