Volume 28, Nº 1 (2019)

The preparation of mAl₂O₃–nYSZ-6 and mAl₂O₃–nYSZ-5 nanocomposite powders (m + n =100 wt%, m = 0–60 wt%) by Impregnation Combustion Synthesis (ICS) with urea as a fuel was studied. Maximal combustion temperatures were measured and calculated for different modes of YSZ introduction. In ICS-produced powders, YSZ particles were found to be covered with an alumina layer.

CaO–Al₂O₃ mixed oxides were prepared by different preparation methods–such as sol–gel, co-precipitation, impregnation, and MW-assisted solution combustion synthesis (M-SCS)–and then impregnated with KOH to examine their activity in transesterification of canola oil to biodiesel. Synthesized nanocomposites were characterized by XRD, FTIR, BET/BJH, and SEM/EDX. The mixed oxides, except those prepared by M-SCS method, exhibited a nearly amorphous structure with some diffraction peaks of calcium oxide. Due to high combustion temperature during the M-SCS process, Ca ions could diffuse into the alumina lattice to form CaAl₂O₄. But upon impregnation with KOH, the former transformed to Ca₁₂Al₁₄O₃₃. The KOH/Ca₁₂Al₁₄O₃₃ nanocatalyst prepared by M-SCS method exhibited better basicity, mean pore size, and activity, as well as highest Ca/Al and K/Al ratios. In the presence of this catalyst, around 86% of canola oil were converted to biodiesel in the transesterification reaction carried out at 65°C, methanol/oil molar ratio 12: 1, 4 wt% catalyst, 4 h. Such parameters seem appropriate for industrial application. The M-SCS method is technically simple, cost effective, time/energy saving and requires no further thermal treatment.

SnO₂:xZn thin films (x = 0, 1, 3, 5, 10, 15 wt%) were deposited onto a glass substrate by ultrasonic spray pyrolysis at 350°C and characterized by XRD, UV–VIS spectra, AFM imaging, and texture analysis. All deposited thin films exhibited preferential orientation along the (110) plane. The films were highly transparent (about 80%) in the visible. Upon an increase in x, the band gap energy of the films decreased from 3.7 eV to 3.3 eV.

Supported polymetallic catalysts (5–15% wt% of active phase) for deep oxidation and hydrogenation were successfully prepared by Self-propagating Surface Synthesis (SSS) using metal nitrates as oxidants and urea as a fuel. Commercial granules of γ-Al₂O₃; NaA, NaX, ZSM-5 zeolites; and silica gel were used as supports. The synthesized catalysts were characterized by XRD, BET, and SEM/EDS. Catalytic behavior of the catalysts in a flow reactor was determined by gas–liquid chromatography, chemical analysis, and tested in deep oxidation of CO and propane as well as in hydrogenation of CO₂ to methane.

Self-propagating high-temperature synthesis is an effective method for preparing refractory ceramic materials, especially carbides and borides as fine powders. The common perception that a pressurized stainless steel reactor is necessary for conducting the synthesis has, until now, excluded it from undergraduate laboratory courses. Our students performed this synthesis using a simple and inexpensive wooden block reactor to prepare TiC, using TiO₂, C and Mg as the reactants. The product at this stage is contaminated with Mg₂TiO₄ which forms through a side-reaction during this highly exothermic reaction. The factors that caused this provoked a stimulating class discussion and led to a method for recovering the TiC as a monophasic powder. The crude and purified product materials were characterized by powder X-ray diffraction. All in all, these aspects make this synthesis an ideal experiment for undergraduate laboratory in chemistry or materials science courses. Moreover, the skills and methods learned through this experiment ensure that students are better equipped to tackle the self-propagating high-temperature synthesis of more complex carbides and refractory ceramic materials in conventional reactors.