What are the catalysts for polyurethane rigid foam and gel reactions?

there are a variety of catalysts used for polyurethane rigid foam reactions and gel reactions, some examples of which are listed below: foaming reaction catalysts: organotin compounds, such as ethylenetrimethylene tin (t-9) and ethylenetriethyltin (t-12). organotin-cobalt composite catalysts, such as ethylenetrimethyltin-cobalt (t-9/co). organotin-acid catalysts, such as ethylenetrimethyltin-benzoic acid (t-9/bzoh). phosphate catalysts such as triphenylphosphine (tpp)…