Disclosed is a method of performing a reaction involving a gaseous reactant stream and a falling film liquid reactant stream by providing a reactor comprising a first multicellular extruded body oriented with its cells extending in parallel in a vertically downward direction from a first end of the body to a second end, the body having a first plurality of cells open at both ends of the body and a second plurality of said cells closed at one or both ends of the body, the second plurality of cells being arranged in one or more groups of contiguous cells and cooperating to define at least in part at least one fluidic passage extending through the body; and further flowing a liquid reactant film down inner surfaces of the first plurality of cells while flowing a gaseous reactant stream up or down the centers of the first plurality of cells while flowing a first heat exchange fluid through the at least one fluidic passage. Various alternative devices for performing the method are also disclosed.