This temperature is when residual oxygen starts to be consumed as well. Apart from the higher onset of acetone evolution the two samples behave similarly. The differences in onset temperatures of acetone and hydrogen evolution are most likely surface area related. In both samples, low amounts of propene are detected as well, starting from 240 °C and 260 °C and climaxing at 485 °C and 515 °C in the smaller and larger crystallite size sample and recognised by the fragment pattern and intensity ratios. Figure shows acetone, hydrogen and carbon monoxide evolution.