Answer: incorrect adverb clause placement
Step-by-step explanation:
The adverb "where" is an adverb of place that expresses where something happens. A catalyst is a word that expresses concrete nouns (in this case, a substance that causes or speeds up a chemical reaction without being affected). Therefore, the clause has an incorrect adverb clause placement. You can fix this sentence by changing it. For instance: A catalyst is a substance which begins the reaction, but does not participate in it. (the adverbial clause immediately after the noun that is being modified)