Heterogeneous catalysis

Question 1

a heterogeneous catalyst is

Answer 1

one that is in a different phase from the reactants

Question 2

adsorption is

Answer 2

the process that occurs when reactants form weak bonds with a solid catalyst

Question 3

desorption is

Answer 3

the process that occurs when products leave the surface of a solid catalyst

Question 4

the catalyst used to make oxygen gas by decomposing hydrogen peroxide solution is usually:

Answer 4

manganese(IV) oxide

this is a heterogeneous catalyst as the manganese(IV) oxide is a solid and the hydrogen peroxide solution a liquid

Question 5

solid heterogeneous catalysts are usually used in ……………….. form or as ……………………. because

Answer 5

• powder form
• or thin coating on an inert support material

-because the action takes place on the surface, so the greater the surface area of the catalyst, the greater their effect

Question 6

the Contact Process is mostly used in the manufacture of

Answer 6

fertilisers

Question 7

the equation for the contact process is:

Answer 7

2SO2 + O2 ⇌ 2SO3

Question 8

the heterogeneous catalyst used in the Contact process is:

Answer 8

vanadium(V) oxide

V2O5

Question 9

the way that a heterogeneous catalyst works is through the three steps:

Answer 9

• adsorption, in which one or more reactants becomes attached to the surface of the catalyst
• reaction, following the weakening of bonds in the adsorbed reactants
• desorption, in which the reaction product becomes detached from the surface of the catalyst

Question 10

the two part process in the Contact process is:

Answer 10

!) V2O5 + SO2 → V2O4 + SO3
sulfur dioxide adsorbs onto the vanadium(V) oxide and a redox reaction occurs
the oxidation number of vanadium decreases from +5 to +4
the sulfur trioxide then desorbs

2) oxygen reacts with the V2O4 on the surface of the catalyst and another redox reaction occurs
V2O4 1/2O2 → V2O5
the original catalyst is regenerated as the oxidation number increases from +4 to +5

Question 11

two of the most significant pollutants from vehicle exhausts are

Answer 11

carbon monoxide and nitrogen monoxide

Question 12

carbon monoxide is a toxic gas that:

it forms:

Answer 12

interferes with oxygen transport from the lungs through the bloostream to vital organs in the body
it forms through the incomplete combustion of hydrocarbon fuels

Question 13

nitrogen monoxide is:

it forms:

Answer 13

easily oxidised in the atmosphere to nitrogen dioxide where it can act as a respiratory irritant and contributes to the formation of acid rain
it forms when nitrogen reacts with oxygen at high temperatures in the internal combustion engine

Question 14

the main transition metals used in catalytic converters are

Answer 14

platinum and rhodium and sometimes palladium

Question 15

the way in which catalytic converters work is:

Answer 15

• the molecules of carbon monoxide and nitrogen monoxide adsorb onto the surface
• their bonds are weakened, and they react together to form carbon dioxide and nitrogen
• the CO2 and N2 then desorb from the surface of the catalyst

Question 16

the overall equation for the action of catalytic converters is:

Answer 16

2CO + 2NO → 2CO2 + N2