ABSTRACT
The CuO-La2O3/ZrO2 catalysts calcined at different temperatures from 500 to 800 °C were studied for the hydrogenation of oxalates to ethylene glycol (EG). Along with the increase of calcination temperatures, the BET surface area, pore volume, and Cu dispersion decreased, whereas the crystallite sizes of Cu species increased. Interestingly, the superior performance such as a 98% selectivity of EG in dimethyl oxalate hydrogenation or a 96.5% selectivity of EG in diethyl oxalate hydrogenation was obtained over the catalyst calcined at 700 °C. Essentially, the surface synergism between Cu species and monoclinic ZrO2 was enhanced by the higher calcination temperature, resulting in the remarkable surface adsorption and activation of H2. Besides, the increase of calcination temperature significantly reduced the surface acidity and basicity, which could effectively suppress the byproduct formation.
ABSTRACT
By combining two n-type groups, pyridine and oxadiazole, with one p-type carbazole group, two novel bipolar hosts, namely 2-(3-(9H-carbazol-9-yl)-[1,1'-biphenyl]-3-yl)-5-(pyridin-2-yl)-1,3,4-oxadiazole (PyOxd-mCz) and 2-(4'-(9H-carbazol-9-yl)-[1,1'-biphenyl]-3-yl)-5-(pyridin-2-yl)-1,3,4-oxadiazole (PyOxd-pCz) have been developed as hosts for blue and green phosphorescent organic light-emitting diodes (PhOLEDs). The two compounds exhibit similar HOMO levels of -5.64 eV for PyOxd-mCz and -5.63 eV for PyOxd-pCz and the same LUMO level of -2.60 eV. With a more twisted configuration due to meta connections, PyOxd-mCz possesses a higher triplet energy level (E T = 2.77 eV) and more balanced carrier transport than PyOxd-pCz (E T = 2.60 eV). PyOxd-mCz hosted devices achieve a peak current efficiency of 39.7 cd A-1 and a maximum EQE of 20.8% with a low turn-on voltage of 3.5 V for FIrpic and 55.2 cd A-1 and 16.4% for Ir(ppy)3. Apart from the appropriate frontier molecular orbital levels and sufficiently high triplet energy of PyOxd-mCz, the more balanced carrier transport plays a key role for excellent device performance.