Tutorial: Physics Topic: Catalyst Prepared by : RNDr. Ondřej Jeřábek Projekt Anglicky v odborných předmětech, CZ.1.07/1.3.09/04.0002 je spolufinancován Evropským sociálním fondem a státním rozpočtem České republiky.
Meaning of exhaust catalyst: Part of boilers or exhaust engines´ sets Changes some poisonous exhaust gases to less harmful ones by catalyst reactions Catalyst chemical meaning: Substance (entering chemical reaction) accelerates or slows down chemical reaction and remains unchanged.
Homogeneous Reactants and catalyst are present in system at the same phase They react with one or more reactants and make chemical intermediate product which reacts to final product Heterogeneous Catalyst is mostly solid and reactants are gaseous This type of catalyst process is used in industry ( there is no need to separate catalyst of reaction mixture).
Catalyst enables chemical reaction in any condition even when it is improbable. In these conditions, thermodynamic balance is different !!! Increasing of required product yield happens by slowing down or by kinetic inability, competing with chemical reaction. This increasing also happens by relative acceleration of demanded chemical reaction, compared with competing one. By diffusion braking of only some products at spill- over active catalyst centres.
Catalyst is used in ignition engines because it is impossible to find mixture composition which would provide high power output. (If the mixture was burnt, the least of pollutant would be made.) Catalyst base is fine structure with large surface of ceramic or steel. Thin catalyst cover applied on catalyst surface (platinum – oxidation, rhodium – reduction) which enables oxidation (at operation temperature 400 – 800 °C) of CO and HC to CO 2 and H 2 O and reduction NO X to N 2.
One of catalyst system components is oxygen search unit λ which reacts to flue gas composition Lambda search unit is feedback for control unit for fuel mixture finishing. For quicker approach and keeping operational temperature, catalyst is fit the most closely to engine or it is heat insulated because there are no reactions except operational temperature and gases with pollutants go out of exhaust.
Catalyst is sensitive to lead presence and petrol entry at longer starting without engine start Catalyst temperature increases by combustion of unburned mixture to 1 000 °C and it is destroyed by exceeding 1400 °C. Catalyst can be used with lead-free petrol because lead contained in fuel would react with catalyst layer which would be destroyed. Catalyst durability of a new car is up to American law-making ´Clean Air´ about 128 000 km
Explain the type of exhaust gases to which are following gases changed: CO a HC
Explain meaning of catalyst and danger of lead petrol for catalyst.
JAN, Zdeněk; ŽDÁNSKÝ, Bronislav ; ČUPERA, Jiří. Automobily 1. Brno : Avid, 2004. 211 s. JAN, Zdeněk; ŽDÁNSKÝ, Bronislav ; ČUPERA, Jiří. Automobily 2. Brno : Avid, 2004. 120 s. JAN, Zdeněk; ŽDÁNSKÝ, Bronislav ; ČUPERA, Jiří. Automobily 3. Brno : Avid, 2004. 220 s. JAN, Zdeněk; ŽDÁNSKÝ, Bronislav ; ČUPERA, Jiří. Automobily 4. Brno : Avid, 2004. 350 s. Translation: www.seznam.cz www.seznam.cz www.slovnik.cz www.slovnik.cz JANATA, Petr. Handy slovník technický anglicko-český a česko-anglický. Plzeň: Nakladatelství Fraus, 2000. ISBN 80-7238-075-3 Lingea LEXIKON 5, Technický slovník anglicko-český a česko-anglický. 2010.