The present invention relates to a method of promoting adsorption of one or more gases to solid particulate material, the method comprising ball milling the solid particulate material (i) in the presence of the one or more gases maintained at a pressure of at least 300 kPa, (ii) using a ratio of milling balls to solid particulate material of at least 60:1, and (iii) at an operating speed of at least 200 rpm.