Catalyst Capital Group Inc. won a bankruptcy auction for Advantage Rent a Car, whose future has been under the microscope since it became a crucial part of antitrust regulators’ decision to bless the merger of two major car-rental firms last year, the Wall Street Journal reported today. The Canadian private-equity firm beat out German rental car company Sixt SE at Monday’s auction, agreeing to forgive up to $46 million in debt it extended to fund Advantage’s chapter 11 case. Advantage filed for bankruptcy protection just months after Hertz Global Holdings Inc. shed the chain so that it could buy Dollar Thrifty Automotive Group Inc. Looking to preserve competition in the highly concentrated $24 billion U.S. car rental industry, the Federal Trade Commission required Hertz to divest Advantage to complete the $2.3 billion purchase of Dollar Thrifty. But just months after the government settlement was reached, Advantage filed for chapter 11 bankruptcy protection with plans to sell itself to the highest bidder.