Can NRF24L01 use IEEE 802.15.4 and 6LoWPAN protocol?
From what I can see the NRF24L01 only supports GFSK modulation, IEEE 802.15.4 requires DSSS, so it can not support 802.15.4.

The CC2520 transceiver was designed for 802.15.4. But if you want an easy life then look at using BeagleBone + CC2531 as the border router and CC2650 Sensor Tags for you nodes. There is very little work needed to get this running see:
http://processors.wiki.ti.com/index.php/Cc26xx_sw_examples

For other 6LowPAN topics including cloud connectivity see:
http://processors.wiki.ti.com/index.php/Contiki-6LOWPAN