Abstract: Trapping, recycling, and other techniques involving catalysts are provided by this invention. The present invention provides for the retention of catalysts and other immobilized entities within a reaction region. In one aspect, the invention promotes such retention by incorporating support material regions including relatively little (or, in some cases, substantially no) catalyst (and thus, a relatively large number of catalyst adsorption sites) which can trap catalyst as it is transported through the downstream support material. In some cases, such arrangements can be achieved by using multiple beds arranged in series. In other instances, the amount of catalyst can be varied within a single bed to achieve the desired effect. The embodiments described herein can be used in systems in which the catalyst is covalently or non-covalently associated with the support surface.