I am an Indian citizen. Can I get 24-hour transit visa on arrival?

Your itinerary is definitely eligible for 24 hour visa free transit and you don't need any kind of visa. As you can see, this is not a visa, but your right to travel without a visa within your eligible itinerary.

You will print out your flight tickets and have those printouts with you. Also, you will declare at check-in in Sydney that you will travel to Bangkok via Beijing using 24 hour visa free transit. After a short inspection of your tickets, you will be allowed to board the plane. During your check-in, you will check whether your luggage will be tagged all the way to Bangkok.

Upon your arrival in Beijing, you will approach 24 hour visa free transit counter where you will apply for a temporary entry permit to be allowed to exit the airport and to explore the city or to have some hours of decent sleep in a hotel. You have to be aware that the issuing of a temporary entry permit always depends on discretion of immigration authorities. Anyway, to increase your chances you are advised to book and accommodation in advance if your layover is during the night hours or a layover tour during the day. If you do one of the mentioned, you should print out a confirmation and have that confirmation with you. This will definitely increase your chances to be granted this permit to a very good level.