Fig. 5. XRD spectra of (a) Cu₂O/Si, (b) CuO/Si, and (c) Cu⁰/Si mixtures after pretreatment and reaction. These mixtures were pretreated at 240 °C for 2 h in a N₂ stream (20 mL min⁻¹) and then reacted at 220, 240, and 260 °C for 1 h, respectively. The reaction conditions: catalyst/Si, 40 g; weight ratios of Cu₂O, CuO, and Cu⁰ to Si, 5 : 100, 5 : 100, and 8 : 100; methanol flow rate, 6 mL h⁻¹.