Supporting information for Remarkable difference in CO2 hydrogenation to methanol on Pd nanoparticles supported inside and outside of carbon nanotubes

Catalyst preparation The CNTs (inner diameter, 5-10 nm; outer diameter, 10-20 nm) were purchased from Chengdu Organic Chemicals. 10 g raw CNTs were refluxed in 500 mL HNO 3 (68 wt%) for 12 h at 140 °C in an oil bath to remove amorphous carbon and the residual catalyst. The suspension was then washed and filtered with deionized water and dried at 110 °C for 12 h. (Some influencing factors were explored; see the supporting information.) For the preparation of the Pd/CNTs-in catalyst, 1 g CNTs were immersed in 25 mL of acetone solution of stoichiometric PdCl 2. The acetone solution was drawn into the channels of the CNTs by capillary forces aided by ultrasonic treatment for 3 h. The mixture was stirred at room temperature for several days until the acetone had completely volatilized and was then dried at 60 °C for 24 h. Although metal selectively deposited inside of the CNTs has been reported in many cases, there are still a lot of unclear factors affecting filling efficiency of metal inside of CNTs. The optimal conditions we have explored are as follow, CNTs: Purity