Correlation between Copper Oxide Particle Size and Selectivity towards Propylene Oxide in Selective Oxidation of Propene

Copper oxide catalysts supported on nanostructured silica SBA-15 were synthesized with varying copper loadings in a range from 1.1 to 19.4wt.%. Catalysts were structurally characterized by N-2 physisorption, X-ray diffraction and ex situ as well as insitu diffuse reflectance UV-Vis spectroscopy. Copper oxide species contained Cu2+ in an octahedral configuration with a tetragonal distortion. Increasing the copper loading resulted in a decreasing optical band gap, which is associated with a growing particle size. Additionally, CuO/SBA-15 samples were examined by temperature-programmed reduction confirming a narrow particle size distribution. Structural evolution and catalytic activity were investigated during selective oxidation of propene focusing on product distribution of nucleophilic and electrophilic oxidation. Catalytic testing was carried out using an on-line GC and MS coupled to a laboratory fixed-bed reactor. All catalysts selectively oxidized propene to acrolein and propylene oxide (PO). With time on stream activity decreased while selectivity towards acrolein and PO increased. While selectivity towards PO increased with copper loading and, hence, copper oxide particle size, selectivity towards acrolein was largely independent of copper loading.