Gas purification apparatus and process

Apparatus useful for purifying a gas stream, comprising

• (a) a shell-and-tube heat exchanger comprising a shell inlet and a shell outlet in fluid communication with the shell inlet, and further comprising a plurality of tubes each having an inlet and an outlet;
• (b) a catalyst system comprising a catalyst supported on a monolithic unitary support having passages therethrough, the support having a length and upstream and downstream ends at opposite ends of the length, wherein the diameter of said support is from one-half to two times the diameter of the shell of the heat exchanger, and wherein the downstream end of said support is connected in fluid communication with the inlets of said tubes by a passageway whose length does not exceed the length of the support and whose diameter is at no point less than the smaller of the diameter of said support and the diameter of said shell;
• and
• (c) a source of gas to be purified in fluid communication with said upstream end of said support.