Ticket booked but can't confirm till getting to Shanghai

hello, I booked a one way from Singapore to Shanghai, and a subsequent one-way starting later the same day from Shanghai to US via 5-hour stop in Tokyo. The two tickets were purchased separately, and are on different airlines, so I cannot confirm my Shanghai-to-US seat till I am in Shanghai. I am a US citizen. Based on the schedule, I would be in Shanghai for 12 hours. Can I utilize either the Visa-free transit or Direct Transit to go out of the airport for a short visit?