Republic of the Philippines Cagayan State University College of Engineering Carig Sur, Tuguegarao City
FINAL REQUIREMENT
CATALYST AND CATALYSIS
Title
INDUSTRIAL CHEMISTRY
Subject
GROUP 13 AGUSTIN, CHARMAINE B. CUSIPAG, JONELOU A. RANTE, FERLYN JADE R.
ENGR. MARIANNE GALVADORES
Professor
CATALYST AND CATALYSIS
I.
CATALYSTS AND CATALYSIS
CATALYSIS
From the Greek kata-, “down,” and lyein, “loosen” Catalysis is the rate of a chemical reaction due to the participation of an additional substance called catalyst. It is an action by catalyst which takes part in a chemical reaction process and can alter the rate of reactions, and yet itself will return to its original form without being consumed or destroyed at the end of the process. With a catalyst, reaction occurs faster and with less energy.
CATALYST
The workhorses of chemical transformations in the industry. Substances that increases the rate of a chemical reaction without itself undergoing any permanent chemical change.
A catalyst is a substance that increases the rate of a chemical reaction by reducing the activation energy, but which is left unchanged by the reaction. (Activation energy: The minimum amount of energy required to initiate a reaction and is denoted by Ea) Most catalysts are solids or liquids, but they may also be gases.
Catalyst: Mechanism
A catalyst permits a different energy pathway for a chemical reaction which has a lower activation energy. The catalyst is not consumed in the chemical reaction.
All catalysts work by lowering the activation energy for a reaction. This is the minimum quantity of energy that reactants must possess to undergo a specific reaction. Most catalysts do this by providing a simpler, less energy-intensive, means for reactant molecules to break bonds and form temporary ones with the catalyst. Catalyst: Characteristics
Activity: The ability of a catalyst to increase the rate of a chemical reaction is called activity. A catalyst may accelerate a reaction to a s high as 1010 times. Selectivity: The ability of a catalyst to direct a reaction to give a particular product. Stability: The number of reactions performed by each active site before it decays or become inactive.
Small quantity: Only small quantity is needed for a reaction.
Specific: One catalyst is need for specific reaction only.
Physical properties may change during a reaction but it does not take part in the reaction.
Catalyst doesn’t influence on the general stoichiometric coefficients.
Catalysts decrease activation energy thus increases the chemical rate.
II.
Catalysts don’t influence on the equilibrium constant. They only reduce time of reaching the equilibrium and increase the rate of forward and back reaction.
HOMOGENOUS CATALYSIS
The process where the reactants are in the same phase (i.e., liquid or gas).
The catalysts are present in the same phase as the substances which are going into the reaction phase.
In chemistry, a homogeneous catalysis is catalysis in a solution b y a soluble catalyst.
Examples of Homogeneous Catalytic Reaction
Name of Process: Hydrolysis of Sugar Catalyst: Hydrogen Ion C12H22O11
+ H2O --------> C6H12O6 +
C6H12O6
The hydrolysis of sugar is catalyzed by H+ ions furnished by sulfuric acid
Name of Process: Lead Chamber for Sulfuric Acids Catalyst: Nitric Oxide 2SO2+O22SO2+O2 ------->NO 2SO32SO3
In the lead chamber process during the manufacture of sulfuric acid, the presence of nitric oxide gas helps in catalyzing the oxidation of sulfur dioxide.
Name of Process: Monsanto Process Catalyst: Rhodium or Iodide CH3OH + CO -------> CH3COOH
III.
Monsanto Process is an industrial method for the manufacture of acetic acid by catalytic carbonylation of methanol.
HETEROGENEOUS CATALYSIS
Heterogeneous catalysis involves the use of a catalyst (solid) from the reactants in a different phase (gas or liquid).
Typical heterogeneous catalysts are inorganic solids such as metals, oxides, sulfides, and metal salts, but they may also be organic materials such as organic hydro peroxides, ion exchangers, and enzymes.
Also called Contact Catalysis (lasted for 100 years).
Important in many areas of the chemical and energy industries.
MODE OF ACTION IN HETEROGENEOUS CATALYSIS 1. Adsorption It’s where a reactant sticks on the surface of the catalyst (active site). The interaction between the surface of a catalyst and the reactant molecules makes them more reactive which causes the weakening of their bonds. Active site – part of a surface which is particularly good at adsorbing things and helping them to react. 2. Reaction At this stage, both of the reactant molecules might be attached to the surface, or one might be attached and hit by the other one moving freely in the gas or liquid. 3. Desorption Simply means that the product molecules break away. This leaves the active site available for a new set of molecules to attach to and react.
Examples of Heterogeneous Catalytic Reaction
Name of the Process: Reduction of nitriles Catalysts: Raney Nickel and ammonia
Nitriles are reduced and the Phenethylamine was synthesize with the presence of Raney nickel and ammonia as a catalyst.
Name of the Process: Haber - Bosch process Catalysts: Iron oxides on alumina
Haber-Bosch is an artificial nitrogen fixation process and is the main industrial procedure for the production of ammonia which is named after its inventors, German chemists Fritz Haber and Carl Bosch.
Name of the Process: Hydrogen Production by Steam Reforming Catalysts: Nickel or K 2O
Methane reacts with steam over a nickel or K 2O (catalyst). The resulting gas is mostly hydrogen but also contains carbon dioxide.
Name of the Process: Hydrogen Cyanide Synthesis (Andrussow Oxidation) Catalysts: Pt-Rh
The Andrussow process is an industrial process for the production of hydrogen cyanide from methane and ammonia in the presence of platinum-rhodium catalyst.
DIFFERENCES BETWEEN HOMOGENEOUS CATALYSIS AND HETEROGENEOUS CATALYSIS
Homogeneous catalysis
Heterogeneous catalysis
These types of catalysts usually are These are found in liquid phase, gas phase common in either liquid phase or gas and solid phase phase Operative temperature for homogeneous Operative temperature for heterogeneous catalysis is generally low except only catalysis is harsh as compared to when under high pressure homogeneous process As the reactants and catalysts are in same The heterogeneous catalysis process phase the diffusion in homogeneous diffusivity is low as the absorbance catalysis process is very high surface is low The heat transfer in homogeneous The heat transfer is relatively low as catalysis is very high as all the molecules compared to homogeneous catalysis as the of reactants and catalysts are in same reactant molecules and catalysts are in
phase
different phase
The active site is very well defined
The active site is not very well defined as different phase sites might have different catalytic properties for the same particle
Recycling methods are not very cost These catalysts although require effective as it’s a long drawn process and reactivating treatment process but still as it’s a difficult treatment method for quite cost effective spent catalysts The modification of heterogeneous Modification of homogenous catalysts is catalysts is relatively difficult as the very easy as it depends upon the tuning of controlling methods of particle site as well electronic and steric properties on metal as the active size at molecular level is really difficult Reaction mechanism is difficult to fins as Reaction mechanism easier to find as the techniques utilised as the product is varied techniques are available scrutinised and not the catalysts Selectivity of homogeneous catalysts are Selectivity of heterogeneous catalysts is very high low
IV.
APPLICATION AND MECHANISM
Widespread application of catalyst enables important reactions to be carried out efficiently in different industries.
GENERAL APPLICATIONS Environmental Applications
Catalyst impacts the environment by increasing the efficiency of industrial processes, but catalyst also plays a direct role in the environment which includes pollution control and reduction.
Specific Applications 1. Three Way Catalytic Converters Catalytic converter (or cat-con) ,found in car’s exhaust system reduce emissions of harmful gases (CO, VOC’s, nitrogen oxides) that are result of the combustion of fuel in
vehicle engines. It is called a catalytic converter because it converts CO into ubiquitous CO2 and Nitrogen oxides into N2 and O2 through chemical reaction on a solid catalyst. Catalyst: Solid Platinum (Pt) or Palladium (Pd) surface unto which reactants from the gaseous phase adsorb and react, Rhodium (Rh)
The process of reaction is assisted by a catalyst that is in a phase different from the reactants, so it is heterogeneous catalysis . Figure: Catalytic Converter- Deconstructed
Main Components are two honeycomb-like monoliths covered with a thin layer of Pt/Rh (first monolith) and Pd/Rh (second monolith). Their role is to increase the exposed surface area covered by the catalyst layer. There are two pipes coming in an out in cat-cons. One of them is Input pipe where it is connected to the engine and brings in hot, polluted fumes from the engine’s cylinders (where the fuel burns and produces power); the second pipe is output pipe connected to the tailpipe. Another component is wash coat which is a carrier for the catalytic materials over a large surface area. Aluminum oxide, titanium dioxide, silicon dioxide or a mixture of silica and alumina can be used. Inside the converter, the gases flow through a honeycomb structure made from a ceramic and coated with the catalysts. Catalyst Role:
One of them tackles Nitrogen oxide pollution using a chemical reaction called reduction . This breaks up nitrogen oxides into nitrogen and oxygen gases (which are harmless). The catalyst for this reaction is Rhodium (Rh)
The other catalyst works by an opposite chemical process called oxidation. And turns carbon monoxide into carbon dioxide. Another oxidation reaction turns unburned hydrocarbons in the exhaust into carbon dioxide and water. The catalyst for these reactions are Platinum (Pt) and Palladium (Pd)
In effect, three different chemical reactions are going on at the same time, that’s why it is called three-way catalytic converters. After the catalyst has done its job, what emerge from the exhaust are mostly nitrogen, oxygen, carbon dioxide, and water (in the form of steam).
Food Processing
One of the most obvious applications of catalysis is the hydrogenation (reaction with hydrogen gas) of fats using Nickel catalyst to produce margarines.
Energy Processing
Petroleum refining makes intensive use of catalysis for alkylation, catalytic cracking (breaking long-chain hydrocarbons into smaller pieces), naphtha reforming and steam reforming (conversion of hydrocarbons into synthetic gas).
Catalysis in Chemical Industry
Catalyst accelerates reactions and thus enable industrially important reactions to be carried out efficiently under practically attainable conditions. Catalytic routes can be designed such that raw materials are used efficiently and waste production is minimized. The chemical industry is largely based upon catalysis. Roughly 85-90 % of all products are made in catalytic process. Industrial processes that rely on Catalysis Reaction Ammonia Synthesis Ammonia Oxidation to NO and HNO 3 Hydrogenation of Vegetable oils Sulfuric Acid
Catalyst Fe Pt-Rh Ni V2O5
V.
REFERENCES http://en.m.wikipedia.org/wiki/Catalytic_converter http://www.explainthatstuff.com/catalytic convrters.html http://www.chemistry.wustl.edu/~edudev/LabTutorials/CourseTutorials?Tutoria ls/AirQuality/CatalyticConverter.html http://en.m.wikipedia.org/wiki/Homogeneous_catalysis Importance of catalysis (pdf) Catalyst and catalysis 3 (pdf) Bhadukmogealy00 (pdf)