Characterization of catalysts

X-ray diffraction data were collected at low angles to obtain information about structural properties of the synthesized materials, i.e., the degree of structural ordering. The XRD method was also used to determine the distance between parallel crystal lattice planes (d₁₀₀) and the distances between mesopore centres (a₀). The elementary cell parameters were determined from the formula: a₀ = d√2. Low-angle X-ray scattering measurements were performed using a Bruker AXS D8 Advance having Johannson monochromator with CuKα radiation, which generated the wavelength of λ = 0.154 nm. All measurements were made with a step 0.02° in the range 2θ = 0.6–8°. Nitrogen adsorption/desorption isotherms and pore size distributions (PSD) were determined at −196 °C with a Quantachrome Nova 1200e analyser. All samples were degassed for 24 hours at 90 °C before the actual measurements. The specific surface area of the samples studied was determined using the BET method and the PSD functions were obtained using the BJH algorithm. Microscopic images of the materials were taken using a transmission electron microscope JEOL JEM-1200 EX II at 80 kV. This type of microscopy was used to determine the degree of ordering of mesopores and their distribution. The TEM image, after setting the scale and threshold for the whole image, were analyzed using “Analyze Particles” option to generate a table with data of the particle areas and diameters. These data were exported into Origin program to construct the histogram plots. The samples were also analysed using a Zeiss scanning electron microscope type EVO at 17 kV. The imaging data were used to evaluate the surface texture and morphology of all synthesized catalysts. Scanning electron microscopy with X-ray energy dispersion option was used to assess the structure of ordered silica modified with transition metal atoms. For this purpose, the LEO 1430 VP microscope (SEM measurement) and Quantax 200 with XFlash 4010 detector by Bruker AXS (EDX) were used. The content of transition metal was determined using inductively coupled plasma optical emission spectrometry with ICP-OES VISTA-MPX spectrometer by Varian. Prior to measurement the samples were mineralized in aqua regia in a microwave oven. Spectroscopic measurements of X-ray excited photoelectrons were performed using the SPECS UHV analysis system with AlK_α radiation (E = 1.487 keV). All samples were neutralized using a low energy electron gun. The measurements permitted determination of the total content of metals in the analysed samples and their oxidation degree.