•Effect of pretreatment on crystal structure transformation of Pd/γ-Al2O3 was studied.•Temperature induced destruction of near-surface PdO is reversible in a short time.•Destruction of PdO intensifies with increasing pretreatment time in inert atmosphere.•Crystal structure is a significant factor on the catalytic activity of Pd/γ-Al2O3.The effects of pretreatment under reducing (H2), inert (N2 and He), and oxidative (air) atmospheres on the catalytic performance of Pd/γ-Al2O3 in benzene degradation were investigated in this study. The crystal structure transformation of Pd active species, which is a significant influencing factor on the catalytic activity of Pd/γ-Al2O3, was investigated in depth via X-ray diffraction combined with in situ Raman analysis. Results showed that the temperature-induced destruction of the near-surface PdO crystal lattice occurs at or above 553 K in inert pretreatment, and this process is reversible when the temperature decreased immediately. The destruction of the PdO crystal lattice largely relied on the increase in treatment time, resulting in the structural transformation from the well-defined crystalline PdO to the amorphous state. The temperature-induced destruction of the near-surface PdO crystal lattice was also observed in oxidative atmosphere with no connection with the increase in treatment time. The catalytic performance of Pd/γ-Al2O3 on benzene degradation is enhanced significantly as a result of the structural transformation from the well-defined crystalline PdO to the amorphous state via pretreatment with inert atmosphere. A possible mechanism for the structural transformation process and its relationship with the catalytic activity is proposed.Download high-res image (188KB)Download full-size image

Microalgae Dunaliella tertiolecta were studied for production of bio-oil through a sub- and supercritical water liquefaction process. The effects of liquefaction temperature, holding time, and feedstock ratio on the yields of the products were investigated. The maximum bio-oil yield is about 36.9%, obtained at a reaction temperature of 360 °C and a holding time of 30 min, with a feedstock ratio of materials to water of 1:10. The various physical and chemical characteristics of bio-oil obtained under the most suitable conditions were determined, and detailed chemical compositional analysis of bio-oil was performed using an elemental analyzer, Fourier transform infrared spectroscopy, and gas chromatography–mass spectrometry. The empirical formula of bio-oil with a heating value of 26.62 MJ kg−1 was established as CH1.38O0.43N0.07, and bio-oil was composed of hexadecanoic acid, palmitamide, and fatty acid methyl ester. Overall, the bio-oil obtained from microalgae Dunaliella tertiolecta were presented as a potentially valuable and environmentally friendly feedstock candidate for biofuels and chemicals.