Hi we plan to visit Beijing from Singapore with a Dutch passport for 4 days.

Unfortunately, itinerary Singapore - Beijing - Singapore is not a transit, so to reach China you will have to apply for Chinese visa or modify your journey by, for example, introducing a layover in Hong Kong during one of your travel legs.

Unfortunately, the route Singapore - Beijing - Singapore is not a transit because there is no third country. Just Singapore and China... So, this itinerary is not eligible for any kind of visa free transit and you should also keep in mind that there is no visa on arrival in Beijing and in most other Chinese cities. You should obtain Chinese visa in advance or change the itinerary to look something like this:

Singapore - Beijing - Hong Kong - Singapore

This is relatively easily obtainable and you will not have to obtain any kind of visa. You can simply buy an open jaw (multi-city) ticket in the form Singapore - Beijing and Hong Kong - Singapore and connect that itinerary with short flight between Beijing and Hong Kong.

Unfortunately, you are not allowed to do that because this is a return trip or a visit to China and there are no elements of transit. In order to travel using your itinerary, you will have to apply for Chinese visa in Singapore or change slightly your flights, of course if possible, so that your itinerary looks something like this:

Singapore - Hong Kong - Beijing - Singapore. As you can see, just by introducing Hong Kong, you immediately become eligible for 144 hours visa free transit because Hong Kong is considered third country for 144 hours rule. Also, instead of Hong Kong, you can introduce Kuala Lumpur or similar options.

Unfortunately, the route Singapore - Beijing - Singapore is not a transit, so you are not eligible for 144 hours visa free transit. In other words, you have to obtain Chinese visa in advance or slightly change your flights. For example, ideal option would be Singapore - Beijing - Hong Kong - Singapore or to replace Hong Kong with Kuala Lumpur. Just try to make some changes and you will be able to travel, stay and explore Beijing visa free.