Yunyi Liu

Synthesis and characterization of hierarchical TiO2 microspheres composed of nanorods: effect of reaction conditions on nanorod density

Urchin-like hierarchical TiO2 microspheres consisting of numerous nanorods were successfully synthesized by a facile hydrothermal process. The effects of reaction conditions (such as additives and reactant concentrations) on TiO2 morphology, particularly on rod density, were systematically investigated. The relationship between rod density and rod diameter was discussed. Based on the above results including a morphological evolution study, a possible mechanism was also proposed to elucidate the growth process of hierarchical TiO2 microspheres using nanorods as building units.

Gaseous ammonia: superior to aqua ammonia in the precipitation of Mg(OH)2 under mild conditions

Aqua ammonia (AA) is frequently used to precipitate various metal hydroxide or oxide particles. Here, we replace AA with gaseous ammonia (GA) to precipitate Mg(OH)2 particles in MgCl2 aqueous solution under mild conditions. The results show that GA can give a higher consistency in the growth of Mg(OH)2 particles although both AA and GA essentially produce Mg(OH)2 by the reaction of Mg2+ with OH−. This work provides results that suggest using ammonia as a precipitant.

Thermochemical processing of fuels involving the use of molecular oxygen

In a high-temperature (e.g., 1000 °C) atmosphere containing combustibles, it is naturally thought that air/O2 should be kept away for fear of combustion and explosion. However, during thermochemical processing (TCP) of carbonaceous fuels (CFs) its actually not that simple. TCP, the process for recovering CFs or converting problematic CFs into preferred ones, is a key technology for efficiently and relatively cleanly utilizing various CFs that supply the majority of the worldwide energy demand. However, TCP is often subject to some obstacles (e.g., high energy input and thermodynamic constraint). This review on extensive literature demonstrates that not only does introducing a controlled amount of O2 (i.e., molecular oxygen) into TCP overcome its many obstacles, but also this O2-assisted strategy is applicable to all of the main CFs currently known. Despite such a wide applicability to CFs, there lacks a comprehensive consideration of various aerobic TCP processes for understanding the O2-assisted strategy as a kind of universal TCP technology for CFs. In this review, we for the first time summarize and discuss the use of O2 in various TCP processes for all of the main CFs. We hope that this review can inspire more consideration of the various aerobic TCP processes so that these extremely complex processes can be communicated or consulted from each others experience/research findings in order to enlighten, guide or promote their respective development.

Greatly changed performance of a metal Pd catalyst by a rather easily formed and removed species–PdHx

Pd catalysts, which are often prepared by reducing Pd salts with NaBH4, have been intensely studied in HCOOH dehydrogenation (FAD) for H2 production. FAD can also be used to hydrogenate or reduce various chemicals by using its in situ generated hydrogen, which exhibits superiority over the direct use of H2 gas. Herein, by using FAD to reduce Cr(VI) as a room-temperature probe reaction, we show that some Pd atoms in the catalyst form PdHx under normal conditions during both catalyst preparation and catalytic reaction (NaBH4 or HCOOH as a hydrogen donor). PdHx greatly hinders Cr(VI) reduction and, interestingly, boosts H2 generation. That is to say, PdHx can be negative or positive species, depending on the focused product. The reason for this phenomenon was also analyzed. Heat treatment for only 10 min can destroy PdHx species and thus, improve the activity for Cr(VI) reduction by up to ∼3 times, which is effective in each catalyst reuse. These findings are critical for controlling the design and functioning of Pd catalyst.

The effect of minerals on the pyrolysis and the combustion of oil shale

ABSTRACT Oil shale (OS) is a particularly promising alternative fossil fuel source. However, very different from coal, its inorganic mineral content is very high. The organic matters (mainly kerogen) are finely distributed in the inorganic minerals. Therefore, the minerals may affect the processing of OS, whose elucidation is critical to the choice of processing conditions. In this work, different minerals (SiO2, CaCO3, and Al2O3) were added to OS with different mass ratios of OS to mineral, respectively. Then, the thermogravimetric (TG) technique was employed to analyze the reaction behavior of these different OS/mineral mixtures in N2 and in air for studying the influence of minerals on the OS pyrolysis in N2 (i.e., retorting) and on the OS combustion in air. The results show that CaCO3 and Al2O3 have a promoting effect on both pyrolysis and combustion of OS, and they can decrease the reaction activation energy of both kinds of processes. However, SiO2 has an inhibitive effect and can increase the reaction activation energy for both kinds of processes. It is hoped that the present study can further increase the understanding toward the effect of different minerals on the OS reactions.