usb-c power adapter for ipad air 2

I use that very combination every day.

iPad Pro models (and the iPad Air3/4) benefit from USB PD (Power Delivery) Fast Charging - and can charge at the higher 18W rate (2.0A @9V or 1.5A @12V). Other models of iPad are limited to charging at 12W (2.4A @5V).

Yes, you can safely use a 30W Power Adapter with your iPad - although your iPad is unlikely to benefit from the higher power rating. Your iPad will only charge at its highest supported rate.