Brother,
Please try to understand that China's leadership is under tremendous pressure.
Yes, China is a powerful country. But China is still not as powerful as the USA in terms of global military dominance. Even Russia is not militarily equal to America. This is reality.
China does not support sanctions. Because anyone with a minimum IQ can understand if Iran is determined to build a nuclear bomb, sanctions will not stop Iran. Did sanctions stop North Korea?
Even the Saudi Arabia is backing sanctions.
See. Thats why I always say don't go by religion all the time. The Uighur separatists are trying to build a Turanian empire splitting Xinjiang from China and they are using Islam as a tool to mislead the international community. The Uighur separatists even killed the Hui Muslims who are the largest Muslim community in China. The Huis came to China also from central Asia, but they don't have any problem with the Chinese identity. But the Uighur separatists have problem...!!! Other Muslim communities like Uzbek, Kazakh, Mongol, Kyrghiz, Tajiks etc etc don't have problem with having the Chinese identity, they don't want separation. And the Uighurs who try to identify themselves with the Turks in a hilarious way, don't look like the Turks of Turkey, I am telling you, if you don't believe me, visit Xinjiang to verify my claims. Look I am an atheist, but if I am given options, I would chose Islam because I have a strong respect for Islamic values. In fact, no religion preaches separation, all religions preach unification of human beings.
Anyway, sorry for being a bit off topic.
Coming to the topic, I would say, is Russia backs the sanction, China will be isolated if China still remains against sanctions. I know China has a veto power. Yes, China can stand against the sanction and use the veto power to block the sanction. But what will happen then?
You know, the US already has prepared its military to bomb Iran round the clock. The B2s will start carpet bombing Iran. Tell me, what will China do then without helplessly watching the destruction of Iran. Be practical, China still does not have any Air craft Carrier, China still has no sophisticated long range bomber like B2, China has a very limited number of submarines. All in all, China military is sufficient for the national protection, but for a long range military projection China is nowhere near the US army. Iran is not a direct neighbor of China, how can China protect Iran from military invasion? Had Iran shared a border with China, of course, I can confidently say, the PLA would have protected you.
We have to accept the realities, brother.