 Houdry later became interested in automotive catalysts, and the catalytic converter was one of approximately 100 patents that he received, but nothing came of it until the 1970s because the tetraethyl lead that was still in use in the 1950s and 1960s poisoned the catalyst.Houdry also invented a catalytic process to produce butadiene from butane gas, which was formed during crude oil production.During World War II, butadiene was important to the production of synthetic rubber.