化学
结晶
催化作用
惰性气体
丙烯醛
钼
无定形固体
钼酸盐
金属
惰性
氧气
Crystal(编程语言)
化学工程
无机化学
结晶学
有机化学
工程类
计算机科学
程序设计语言
标识
DOI:10.1016/0021-9517(82)90269-x
摘要
A high-temperature, controlled-atmosphere X-ray diffractometer was used to measure rates of crystallization of a mixed metal molybdate catalyst. The catalyst, initially amorphous, becomes crystalline at temperatures of 400–500 °C. This occurs slowly in inert atmospheres and much more rapidly in air. After thermal treatment in air, relative acrolein oxidation activity is proportional to the fraction of the catalyst which remains uncrystallized. The phases observed in air include V2O5, MnMoO4, and MoO3. The phases crystallizing in inert atmospheres are MnMoO4, Mo4O11, W18O49, and V4O9. Unidentified phases remain in both cases. Crystallization follows a second-order rate law, with a rate constant of 7 × 10−3 hr−1 in dry air at 410 °C. Water vapor in air, even at 10–20 ppm, increased the rate markedly. In inert atmospheres, H2O has no effect. The initially active catalyst probably contains compounds similar to molybdenum shear structures. Crystallization in air proceeds by an annealing out of oxygen vacancy defects and subsequent crystal growth.
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