Field Emission Microscopy Study of Supported Bimetallic Catalysts Pd-Mo/Al2O3/W: Nitrogen Spillover

Šotola, Jan; Knor, Z.

doi:10.1006/jcat.1994.1060

Cited by 12 publications

(3 citation statements)

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“…This was demonstrated in FEM/FIM studies with Pd and Mo layers successively deposited on a WO x substrate in UHV conditions. In a more recent study, the nitrogen spillover process could be demonstrated for a Pd − Mo/Al 2 O 3 / W surface prepared on a tungsten tip and using alumina, which is one of the important carrier materials in catalysis [127]. Islands of molybdenum metal were found to be active in the dissociative trapping of nitrogen molecules.…”

Section: Modeling Structures and Interfacial Transport Processesmentioning

confidence: 99%

Heterogeneous Catalysis and High Electric Fields

Kruse

Bocarmé

2008

Handbook of Heterogeneous Catalysis

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Introduction The relationships between high electric fields and heterogeneous catalysis are twofold: First, high electric fields are applied in field emission and field ion microscopes and related methods. These techniques can provide detailed in situ information on catalytic surface processes with a lateral resolution on the atomic scale. Second, high electric fields can affect the surface properties of solids. Electronic and structural parameters are frequently field dependent and influence chemisorption processes of molecules and also catalytic activity and reaction pathways of surface reactions.High electric fields, defined as fields of the order of some tens of volts per nanometer, are what valence electrons in atoms and molecules experience and what these electrons are exposed to on adsorption at solid surfaces. Thus, these fields are ubiquitous in chemistry and form, in the context of this contribution, an intimate part of heterogeneous catalysis. Quantum mechanical aspects of chemical bonding of solid surfaces distinguish between shortrange covalent and long-range electrostatic contributions. These long-range effects create an electrostatic Coulomb potential which causes changes in ionization potentials and electron affinities of adsorbed molecules. As a consequence, catalytic surface reactions may be altered. However, in real catalysts it is sometimes difficult to distinguish between contributions of local binding and long-range electrostatic fields.Long-range fields of the order of 10 V nm −1 are generated in a controlled manner in the field ion microscope, originally developed by Muller [1] for imaging * Corresponding author.

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Section: Modeling Structures and Interfacial Transport Processesmentioning

confidence: 99%

Heterogeneous Catalysis and High Electric Fields

Kruse

Bocarmé

2008

Handbook of Heterogeneous Catalysis

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“…If a suitable desorption surface is put in contact with the catalyst, spillover of nitrogen could enhance the rate of reaction. Palladium has been reported to be a receiver for spillover nitrogen from molybdenum and tungsten [136,137]. If it can also receive the nitrogen atoms from the nickel catalyst in this research, it will increase the rate that active sites are made available on the catalyst.…”

Section: Table 125: Reaction Schemes For Dehydrogenation With Permeation [28]mentioning

confidence: 80%

“…If recombinative desorption of nitrogen became the limiting step, Hydrogen From Ammonia By Catalytic Spillover Membrane experiments with these could explored. Also palladium itself has the potential to receive spillover nitrogen [136,137] , which could alleviate this potential bottleneck. If dehydrogenation of ammonia becomes rate limiting then alternate catalysts could be explored, either ruthenium or an iron-nickel alloy [67].…”

Section: Future Workmentioning

confidence: 99%

Hydrogen from Ammonia by Catalytic Spillover Membrane

Tailby¹

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<p>One of the major challenges to be overcome before hydrogen fuelled vehicles can become commonplace is to store hydrogen with sufficient storage density to be practical. One approach to overcoming this challenge involves converting the hydrogen into a secondary fuel that can be stored more easily, such as ammonia. This introduces the challenge of efficiently retrieving the hydrogen from the secondary fuel with sufficient purity to be used in a polymer electrolyte membrane fuel cell. Putting the hydrogen producing reaction inside a membrane which is capable of filtering out hydrogen creates a membrane reactor which can increase hydrogen purity and can accelerate the reaction both kinetically and thermodynamically. The most effective materials currently known for hydrogen membranes are high palladium alloys of copper and silver. These are able to absorb hydrogen on the side with high hydrogen partial pressure and desorb that hydrogen on the side with low hydrogen pressure. Palladium metal is also able to interact with some catalysts by hydrogen spillover. Hydrogen is transported from the surface of the catalyst to the palladium surface more quickly than the hydrogen can desorb from the catalyst, this potentially accelerates both the catalysis and the hydrogen filtration. This research aimed to create a catalytic spillover membrane to extend the possibility of ammonia as a secondary fuel for hydrogen transport. In this research, several methods to produce a nickel catalyst on the surface of the palladium were explored: electrodeposition with and without a lithographic template; spray coating with nanoparticles; and preshaped nickel mesh and nickel foam. These potential catalysts were tested for ammonia decomposition. Templated electrodeposition created the most effective catalyst, but the nickel foam was most easily applied to the next stage of the research. The nickel foam catalyst was subsequently retested for ammonia decomposition in three scenarios: in contact with palladium foil; in a reactor with a palladium membrane; and in contact with a palladium membrane. The presence of a palladium membrane improved decomposition more than spillover contact between nickel foam catalyst and palladium, however, the combination of spillover contact with a palladium membrane increased the ammonia decomposition further. The rate of hydrogen flux through the palladium membranes was calculated for the experimental results. These were compared to flux values predicted by a model equation. The results showed that spillover contact between nickel catalyst and palladium membrane increased the hydrogen flux through the membrane.. The research outcomes have generated new knowledge and improved understanding of the morphology and role of nickel catalysts in accelerating ammonia decomposition. The research highlights the complex relationship between reactor design, gas flow paths, catalyst presentation and catalysis chemistry, suggesting promising areas for future research.</p>

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