Catalytic CO oxidation on Pt(111) to CO2 was studied under atmospheric pressures of CO and O2 and at various temperatures. Surface vibrational spectroscopy by sum frequency generation was used to probe the surface species, while the reaction rate and gas composition were simultaneously monitored by gas chromatography. Correlation between the turnover rates and the surface coverage of various CO species were utilized to identify the active CO species in the reaction. Ignition, above which the reaction becomes self-sustained, divides the reaction into two reactivity regimes. Below ignition, atop bonded CO appears as the major species on the surface, but the reaction rate is inversely proportional to the surface coverage of this species, indicating that it is not the active species but rather an inhibitor. The observed activation energy for the reaction in this regime suggests that desorption of atop CO is the rate-limiting step in the reaction. Above ignition, the atop CO becomes hardly detectable and the a...

High-pressure co oxidation on pt(111) monitored with infrared-visible sum frequency generation (sfg)

Oscillatory reactions on single crystal surfaces

The article contains sections titled:



1.	Introduction	
1.1.	Types of Catalysis	
1.2.	Catalysis as a Scientific Discipline	
1.3.	Industrial Importance of Catalysis	
1.4.	History of Catalysis	
2.	Theoretical Aspects	
2.1.	Principles and Concepts	
2.1.1.	Sabatier's Principle	
2.1.2.	The Principle of Active Sites	
2.1.3.	Surface Coordination Chemistry	
2.1.4.	Modifiers and Promoters	
2.1.5.	Active Phase – Support Interactions	
2.1.6.	Spillover Phenomena	
2.1.7.	Phase-Cooperation and Site-Isolation Concepts	
2.1.8.	Shape-Selectivity Concept	
2.1.9.	Principles of the Catalytic Cycle	
2.2.	Kinetics of Heterogeneous Catalytic Reactions	
2.2.1.	Concepts of Reaction Kinetics (Microkinetics)	
2.2.2.	Application of Microkinetic Analysis	
2.2.3.	Langmuir – Hinshelwood – Hougen – Watson Kinetics	
2.2.4.	Activity and Selectivity	
2.3.	Molecular Modeling in Heterogeneous Catalysis	
2.3.1.	Density Functional Theory	
2.3.2.	Kinetic Monte Carlo Simulation	
2.3.3.	Mean-Field Approximation	
2.3.4.	Development of Multistep Surface Reaction Mechanisms	
3.	Development of Solid Catalysts	
4.	Classification of Solid Catalysts	
4.1.	Unsupported (Bulk) Catalysts	
4.1.1.	Metal Oxides	
4.1.1.1.	Simple Binary Oxides	
4.1.1.2.	Complex Multicomponent Oxides	
4.1.2.	Metals and Metal Alloys	
4.1.3.	Carbides and Nitrides	
4.1.4.	Carbons	
4.1.5.	Ion-Exchange Resins and Ionomers	
4.1.6.	Molecularly Imprinted Catalysts	
4.1.7.	Metal – Organic Frameworks	
4.1.8.	Metal Salts	
4.2.	Supported Catalysts	
4.2.1.	Supports	
4.2.2.	Supported Metal Oxide Catalysts	
4.2.3.	Surface-Modified Oxides	
4.2.4.	Supported Metal Catalysts	
4.2.5.	Supported Sulfide Catalysts	
4.2.6.	Hybrid Catalysts	
4.2.7.	Ship-in-a-Bottle Catalysts	
4.2.8.	Polymerization Catalysts	
4.3.	Coated Catalysts	
5.	Production of Heterogeneous Catalysts	
5.1.	Unsupported Catalysts	
5.2.	Supported Catalysts	
5.2.1.	Supports	
5.2.2.	Preparation of Supported Catalysts	
5.3.	Unit Operations in Catalyst Production	
6.	Characterization of Solid Catalysts	
6.1.	Physical Properties	
6.1.1.	Surface Area and Porosity	
6.1.2.	Particle Size and Dispersion	
6.1.3.	Structure and Morphology	
6.1.4.	Local Environment of Elements	
6.2.	Chemical Properties	
6.2.1.	Surface Chemical Composition	
6.2.2.	Valence States and Redox Properties	
6.2.3.	Acidity and Basicity	
6.3.	Mechanical Properties	
6.4.	Characterization of Solid Catalysts under Working Conditions	
6.4.1.	Temporal Analysis of Products (TAP Reactor)	
6.4.2.	Use of Isotopes	
6.4.3.	Use of Substituents, Selective Feeding, and Poisoning	
6.4.4.	Spatially Resolved Analysis of the Fluid Phase over a Catalyst	
6.4.5.	Spectroscopic Techniques	
7.	Design and Technical Operation of Solid Catalysts	
7.1.	Design Criteria for Solid Catalysts	
7.2.	Catalytic Reactors	
7.2.1.	Classification of Reactors	
7.2.2.	Laboratory Reactors	
7.2.3.	Industrial Reactors	
7.2.4.	Special Reactor Types and Processes	
7.2.5.	Simulation of Catalytic Reactors	
7.3.	Catalyst Deactivation and Regeneration	
7.3.1.	Different Types of Deactivation	
7.3.2.	Catalyst Regeneration	
7.3.3.	Catalyst Reworking and Disposal	
8.	Industrial Application and Mechanisms of Selected Technically Relevant Reactions	
8.1.	Synthesis Gas and Hydrogen	
8.2.	Ammonia Synthesis	
8.3.	Methanol and Fischer – Tropsch Synthesis	
8.3.1.	Methanol Synthesis	
8.3.2.	Fischer – Tropsch Synthesis	
8.4.	Hydrocarbon Transformations	
8.4.1.	Selective Hydrocarbon Oxidation Reactions	
8.4.1.1.	Epoxidation of Ethylene and Propene	
8.4.1.2.	Ammoxidation of Hydrocarbons	
8.4.2.	Hydroprocessing Reactions	
8.5.	Environmental Catalysis	
8.5.1.	Catalytic Reduction of Nitrogen Oxides from Stationary Sources	
8.5.2.	Automotive Exhaust Catalysis

Heterogeneous Catalysis and Solid Catalysts

Chemical kinetic modeling in heterogeneous catalysis is advancing in its ability to provide qualitatively or even quantitatively accurate prediction of real-world behavior because of new advances i...

Progress in Accurate Chemical Kinetic Modeling, Simulations, and Parameter Estimation for Heterogeneous Catalysis

On the microscale, migration, proliferation and death are crucial in the development, homeostasis and repair of an organism; on the macroscale, such effects are important in the sustainability of a population in its environment. Dependent on the relative rates of migration, proliferation and death, spatial heterogeneity may arise within an initially uniform field; this leads to the formation of spatial correlations and can have a negative impact upon population growth. Usually, such effects are neglected in modeling studies and simple phenomenological descriptions, such as the logistic model, are used to model population growth. In this work we outline some methods for analyzing exclusion processes which include agent proliferation, death and motility in two and three spatial dimensions with spatially homogeneous initial conditions. The mean-field description for these types of processes is of logistic form; we show that, under certain parameter conditions, such systems may display large deviations from the mean field, and suggest computationally tractable methods to correct the logistic-type description.

/pdf/correcting-mean-field-approximations-for-birth-death-3uqpox4csn.pdf

Correcting mean-field approximations for birth-death-movement processes.

A model for the catalytic oxidation of CO on fractal lattices

We study a model of the CO oxidation on percolation clusters which represent the surface of our system in the Monte Carlo simulation. We observe two phase transitions where the surface is completely covered (poisoned) by one species (in our system CO or O). These phase transitions are described by their order and the values of the mole fraction yCO of CO in the gas phase at y1 (O poisoning) and at y2 (CO poisoning). The interval (y1,y2) represents the reactive regime. The influence of the occupation probability p for generating a spanning cluster on the underlying square lattice, of the diffusion of CO and of the lattice size on the value and the character of the kinetic phase transitions is studied. Increasing p leads to a shift of y2 to larger values of yCO for all ratios of adsorption to diffusion events but the value of y1 is increased to a larger value of yCO only if diffusion is not allowed. In the case of diffusion the value of y1 is maximally independent of p. A change in the character of the phas...

A Monte Carlo simulation of the CO oxidation on probabilistic fractals

In this paper the effects of physisorption and of the Eley-Rideal mechanism on a surface reaction model which describes the catalytic oxidation of CO on a metal catalyst are discussed. The physisorption causes a shift in the value of the second-order phase transition y 1 (at which the surface of the catalyst is completely covered by O) to y CO = y 1 = 0.28 from its value of y 1 absence of physisorption. The value of the first-order phase transition y 2 (complete covering with CO) is not affected by the physisorption and remains at Y CO = y 2 = 0.650. y CO represents the mole fraction of CO molecules in the gas phase. For this simu a mean-field ansatz is introduced which is able to describe the reaction system to a certain degree. This ansatz results in y 1 = 0 and y 2 = 0.57 indicating that the second-order phase transition at y 1 is dominated by long-range correlations and is not mean-field character. The influence of the Eley-Rideal mechanism as an additional step for the formation of CO 2 changes the behaviour of the reaction system dramatically: the second-order phase transition at y 1 (which is not observed experimentally) vanishes ( y 1 = 0) and the first-order phase transition is shifted to y 2 = 0.646. From this simulations we are able to give an alternati way to understand why O-poisoning is not experimentally observed.

The influence of physisorption and the Eley-Rideal mechanism on a surface reaction : CO+O2

In this paper we introduce a stochastic model for the A+1/2B2→0 reaction on a square lattice. Reaction between an A and a B particle occurs if they are nearest neighbors on the lattice. To this system which includes adsorption and reaction steps we add the effect of A‐diffusion and A‐desorption. We describe the model in terms of master equations using the Markovian behavior of the system. The equations are truncated at a certain level via a modified Kirkwood approximation. The reaction is in this paper introduced between particles which are nearest neighbors on the lattice. This approach which is different from a previous article [J. Mai et al., J. Chem. Phys. 98, 10017 (1993)] requires a special treatment of the stochastic equations and the correlation functions. In particular the Kirkwood superposition approximation, which is used to truncate the hierarchy of equations, has to be modified. The resulting system of lattice equations is solved in a small region around a reference point. The solution is con...

Stochastic model for the A+B2 surface reaction: Island formation and complete segregation

A Monte Carlo simulation for the catalytic oxidation of CO on DLA clusters

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