By Jonathan Stempel (Reuters) – U.S. authorities on Wednesday said they have taken down a nationwide ring to steal thousands of catalytic converters from cars and trucks, charging 21 people and seizing millions of dollars in assets. Various defendants were accused in separate indictments unsealed in Sacramento, California, and Tulsa, Oklahoma, of crimes such as transporting and receiving stolen goods across state lines, and conspiring to commit money laundering. Catalytic converters are vehicle exhaust devices that convert toxic gases into safer emissions. They can be stolen in less than one m…