Catalysts characteristics seminar

INTRODUCTION:

CATALYSIS :

Catalysis 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 reaction.

A substance which changes the speed of a reaction without being used itself is called a catalyst.

If а catalyst increases (accelerates) the speed of а reaction, it is called а positive catalyst and the phenomenon is called positive catalysis. On the other hand, if а catalyst decreases (retards) the speed of а reaction, it is called а negative catalyst and the phenomenon is called negative catalysis.

1. SEMINAR ON : CHARACTERISTICS OF CATALYSTS Prepared By : MAHASWARI JOGIA CATALYTIC REACTION ENGINEERING HCE 23 4/13/2017 1 DSCE,CHEMICAL DEPT.

2. 4/13/2017 2 DSCE,CHEMICAL DEPT. CONTENTS: INTRODUCTION CATALYST CHARACTERIZATION: POROSITY ACTIVITY SELECTIVITY SPECIFICITY DECREASE ACTIVATION ENERGY CATALYST POISINING CATALYSTS PROMOTERS INDUSTRIAL IMPORTANCE OF CATALYSTS REFERENCES

3. INTRODUCTION: CATALYSIS : Catalysis 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 reaction. A substance which changes the speed of a reaction without being used itself is called a catalyst. If а catalyst increases (accelerates) the speed of а reaction, it is called а positive catalyst and the phenomenon is called positive catalysis . On the other hand, if а catalyst decreases (retards) the speed of а reaction, it is called а negative catalyst and the phenomenon is called negative catalysis. 4/13/2017 3 DSCE,CHEMICAL DEPT.

4. CATALYST CHARACTERIZATION : Characterization of heterogeneous catalyst refers to the determination of its physical and chemical characteristics, which are responsible for its performance in a reaction. Characteristics of catalysts include: porosity selectivity activity amount required specificity decrease the activation energy catalytic promoters catalytic poisons 4/13/2017 4 DSCE,CHEMICAL DEPT.

5. POROSITY : The porous structure enables the solid to have a total surface much higher. Most common catalysts have a specific surface area between 1 and 1000 m 2 g-l, while their external specific surface area is in the range 0.01-10 m2 g-l . The pores are classified in different classes depending on their size: 1. Micro pores (+ < 2 nm), 2. Mesopores (2 < D < 50 nm), 3. M acro pores (D> 50 nm). A catalyst that has a large area resulting from pores is called porous catalyst. Sometimes pores are very small they will prevent large ones from entering. This is called molecular sieve. These sieves can form basis for quite selective catalysts, the pores control the residence time of various molecules near the active sites. 4/13/2017 5 DSCE,CHEMICAL DEPT.

6. ACTIVITY. The ability of a catalyst to increase the rate of a chemical reaction is called activity. A catalyst may accelerate a reaction to as high as 10^10 times. Catalyst has an ability to increase the rate of reaction. This ability of catalyst is known as the activity of catalyst. It depends upon adsorption of reactants on the surface of catalyst. Chemisorption is the main factor governing the activity of catalysts. The bond formed during adsorption between the catalytic surface and the reactants must not be too strong or too weak. It must be strong enough to make the catalyst active whereas, not so strong that the reactant molecules get immobilized on the catalytic surface leaving no further space for the new reactants to get adsorbed. 4/13/2017 6 DSCE,CHEMICAL DEPT.

7. SELECTIVITY. The ability of the catalyst to direct a reaction to give a particular product. Selectivity serves as the measure of specificity of catalysts and is estimated by the ratio of the specific reaction rate to the general transformation rate of the initial substances in the presence of a given catalyst. SMALL QUANTITY : Only small quantity is need for a reaction . Hence making it very efficient to use and handle. Also it makes it at a reliable cost to use for larger productions. 4/13/2017 7 DSCE,CHEMICAL DEPT.

8. S PECIFIC ITY : One catalyst is need for specific reaction only . The most important property of catalysts is specificity of action; that is, each chemical reaction or group of uniform reactions can be accelerated only by very specific catalysts. Catalyst specificity is most clearly manifested in that catalysts can determine the course of the reaction. Example are enzymes specific to substrate they react to. 4/13/2017 8 DSCE,CHEMICAL DEPT.

9. LOWER ACTIVATION ENERGY: Catalysts decrease activation energy thus increases the chemical rate. Adding a catalyst has exactly this effect on activation energy. A catalyst provides an alternative route for the reaction. That alternative route has lower activation energy. 4/13/2017 9 DSCE,CHEMICAL DEPT.

10. CATALYTIC PROMOTERS: Substances which themselves are not catalysts, but when mixed in small quantities with the catalysts increase their efficiency are called as promoters or activators . For example, in Haber’s process for the synthesis of ammonia, traces of molybdenum increases the activity of finely divided iron which acts as a catalyst. EXPLANATION OF PROMOTION ACTION: - Change of lattice spacing Increase of peaks and cracks Note : The phenomenon of promotion is a common feature of heterogeneous catalyst. 4/13/2017 10 DSCE,CHEMICAL DEPT.

11. CATALYTIC POISONS: If the absorbed species are very stable, and much energy is release in the chemisorption process, the absorbed species are not reactive. Their absorptions prevent further absorption of other species, making the catalyst inactive. Substances which destroy the activity of the catalyst by their presence are known as catalytic poisons . For example, the presence of traces of arsenious oxide in the reacting gases reduces the activity of platinized asbestos which is used as catalyst in contact process for the manufacture of sulphuric acid. 4/13/2017 11 DSCE,CHEMICAL DEPT.

12. EXAMPLE: Contact Process SO2+O2 → 2SO3 (Pt, As2O3) Haber Process N2+3H2→2NH3 (Fe, H2S ) Synthesis of Water 2H2+O2→2H2O (Pt, CO) The poison is adsorbed on the catalyst surface in preference to the reactants. The catalyst may combine chemically with impurity. EXPLANATION OF CATALYTIC POISONING: Fe+H 2 S→FeS+H 2 FIG 2: POISONING OF PLATINUM CATALYST

13. INDUSTRIAL IMPORTANCE OF CATALYSTS Much fundamental and applied research is done by industrial companies and university research laboratories to find out how catalysts work and to improve their effectiveness. C atalytic activity can be improved, it may be possible to lower the pressure at which the process operates and thus save fuel which is one of the major costs in a large-scale chemical process. It is cost and energy efficient means for the production of a broad range of petroleum refining, chemical products, pharmaceuticals and for environmental protection. Catalysts speed up the rate of reaction, which saves money because the plant doesn't have to operate for as long to produce the same amount of product. Catalysts allow the reaction to work at a much lower temperature. This reduces the energy used up in a reaction which is good for sustainable development. 4/13/2017 13 DSCE,CHEMICAL DEPT.

14. 4/13/2017 DSCE,CHEMICAL DEPT. 14 Achieving better process economics and productivity Increase reaction rates - fast Simplify the reaction steps - low investment cost Carry out reaction under mild conditions (e.g. low T, P) - low energy consumption Reducing wastes Improving selectivity toward desired products - less raw materials required, less unwanted wastes Replacing harmful/toxic materials with readily available ones Producing certain products that may not be possible without catalysts Having better control of process (safety, flexible etc.) Encouraging application and advancement of new technologies and materials

15. REFERENCES 4/13/2017 DSCE,CHEMICAL DEPT. 15 http://www.essentialchemicalindustry.org/processes/catalysis-in-industry.html http://encyclopedia2.thefreedictionary.com/Catalysts http://www.chemguide.co.uk/physical/basicrates/catalyst.html http://byjus.com/chemistry/activity-selectivity-of-catalyst/ http://nptel.ac.in/courses/103103026/11 https://www.google.co.in/search?q=advantages++ of+catalysts&hl=en&authuser=0&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjR0cuk3p_TAhVEtI8KHfNoBiMQ_AUICCgB&biw=1366&bih=635#imgrc=UfPwF3UFT6yaTM www.slideshare.com/catalysis https://books.google.co.in/books?id=YPzKuXIfxfcC&pg=PA443&dq=advantages++of+catalysts&hl=en&sa=X&ved=0ahUKEwiG2IKl4J_TAhXEo48KHYjpAocQ6AEIGzAA#v=onepage&q=advantages%20%20of%20catalysts&f=false elements of chemical eaction engineering by H.SCOTT FOGLER

16. THANKYOU!!!! 4/13/2017 16 DSCE,CHEMICAL DEPT.