9701 · 26.2
Homogeneous and heterogeneous catalysts — FAQ
Frequently asked questions for 9701 Homogeneous and heterogeneous catalysts. Direct answers first, then deeper explanation — then practise with marking.
If a catalyst is regenerated, why do industries need to replace their catalysts?
Although catalysts are chemically regenerated in each cycle, they degrade physically and chemically over time. Heterogeneous catalysts can be deactivated by poisoning (where impurities block active sites) or sintering (where high temperatures cause particles to fuse, reducing surface area). This loss of activity eventually makes it more economical to replace the catalyst.
How exactly does a catalyst provide an 'alternative pathway'?
It offers a different set of elementary steps for the reaction to proceed. For a homogeneous catalyst, this involves forming a new intermediate species. For a heterogeneous catalyst, it involves binding reactants to a surface, which weakens their internal bonds and holds them in a favourable orientation for reaction. Both these new pathways have lower activation energies than the uncatalysed route.
What is autocatalysis and how does it differ from regular catalysis?
Autocatalysis is a specific type of catalysis where one of the reaction products acts as the catalyst for the reaction. A classic example is the reaction between manganate(VII) ions and ethanedioate ions, where the Mn²⁺(aq) product catalyses its own formation. Unlike a typical catalysed reaction which is fastest at the start, an autocatalysed reaction starts slowly and then accelerates as the concentration of the catalytic product increases.