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

Abstract

Copper oxide catalysts supported on nanostructured silica SBA‐15 were synthesized with varying copper loadings in a range from 1.1 to 19.4 wt.%. Catalysts were structurally characterized by N2 physisorption, X‐ray diffraction and ex situ as well as in situ 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.

Propylene Epoxidation using Molecular Oxygen over Copper- and Silver-Based Catalysts: A Review

“…(A) PO productivity enhancement achieved over silver (black symbols)- and copper-based catalysts (red symbols) using different strategies: doping by alkalis, halides, or both ,,,− ,,,,,− (squares), support effects ,,, (downward triangles), particle size effects, ,,,, (upward triangles), particle shapes ,, (circles), and engineering approach ,,,,,− (stars). (B) PO selectivity as a function of particle size for copper (red triangles)- and silver-based catalysts (black triangles).…”

“…This effect has been noticed and examined by several researchers. 73,84,96,97 The common thread is that acidic supports, even if they exhibit moderate Lewis acidity such as amorphous silica, 18,73,86,98 should be avoided. If an acidic support is used, it should be modified, where the acid sites are neutralized by titrating with a basic promoter.…”

“…Exceptional results were reported over Ag/WO 3 nanorod catalysts with PO yields of about 15%, obtained at 20 bar reaction pressure. 41 The same authors were able to improve 16,19,20,22−24,61,65,66,74,82−86 (squares), support effects 14,31,42,75 (downward triangles), particle size effects, 28,41,80,83,86 (upward triangles), particle shapes 11,14,43 (circles), and engineering approach 33,34,37,41,74,107−109 the performance of their 5 wt % Ag/WO 3 nanorod catalyst to 45% PO yield when the reaction was operated at 30 bar and 375 °C. 109 In addition to activity and PO selectivity, PO productivities in excess of 1 g PO/(g cat h) are required for industrial application.…”

“…Diekmann et al 86 studied the effect of copper oxide particle size supported over SBA-15 on PO selectivity. According to their UV−vis analysis, increasing the Cu loading from 1.1 to 19.4 wt % increased the CuO cluster size from predominantly single-atom Cu 2+ centers to nanometer-scale particles, presumably smaller than 3 nm.…”

Xylitol Production from Xylose by Catalytic Hydrogenation over an Efficient Cu–Ni/SiO2 Bimetallic Catalyst

“…Several overlapped peaks ranging from 200 to 400 °C are observed for 20Cu/SiO 2 , likely due to the reduction of copper oxide with different particle sizes on the support. 36,37 Several broad H 2 consumption peaks between 250 and 500 °C appear for the 20Ni/SiO 2 catalyst due to the presence of inhomogeneous NiO with various particle sizes that have different interactions with the support. 38 For bimetallic catalysts, the reduction peaks shifted definitely to a much lower temperature.…”