What is heterogeneous catalysis in gas phase?
&quot;Gas phase&quot; means that the reactants are gases
The basic answer is that heterogeneous catalysis &quot;in the gas phase&quot; just means that the materials being reacted are gases. They catalysts can be liquids or solids (more common).
A simple, but very, very important example is the reaction used to convert ammonia into nitric acid (vital for fertiliser production, important for many organic chemistry building blocks and explosives). In this reaction gaseous mixtures of air and ammonia are passed over platinum gauze and, initially, produce NO (nitric oxide) which is further oxidised homogeneously to dinitrogen tetroxide which ultimately reacts with water to give nitric acid. A good summary of the reaction and its history is given in this Johnson Matthey article.
So gas-phase reactants + solid catalyst -&gt; product. Gas phase heterogeneous catalysis.