Lopatin Sergey I, Shugurov Sergey M, Panin Andrej I
Institute of Chemistry, St. Petersburg State University, Universitetskii pr. 26, 198504, Saint Petersburg, Russia.
Rapid Commun Mass Spectrom. 2016 Sep 30;30(18):2027-32. doi: 10.1002/rcm.7677.
BaCeO3 species, which are known to be excellent proton conductors, are potential candidates as electrolytes in hydrogen concentrators and fuel cells. Oxides of barium and cerium, with their reactivity can, in turn, form gaseous associates - complex molecules with two different types of atoms (not including oxygen). To predict the possibility of the existence of gaseous associates formed by barium and cerium oxides it is important to know their thermodynamic characteristics. Until the present investigation, gaseous cerates were unknown.
High-temperature Knudsen effusion mass spectrometry was used to determine the partial pressures of vapor species over the BaO-CeO2 system, and the formation enthalpies of gaseous CeO2 and BaCeO3 were derived. Measurements of partial pressures and reaction enthalpies were performed with a MS-1301 mass spectrometer. Vaporization was carried out using molybdenum and tungsten effusion cells containing the samples under study and pure gold as a reference substance. A theoretical study of gaseous cerium dioxide and barium cerate was performed by several quantum chemical methods: DFT M06, DFT PBE0 and MP2.
In the temperature range 1900-2120 K, CeO and CeO2 were found to be the main vapor species over the solid CeO2 . Ba, BaO, CeO, CeO2 and BaCeO3 species were found in the vapor over the BaO-CeO2 mixture. On the basis of the equilibrium constant of the gaseous reaction BaO + CeO2 = BaCeO3 , the standard formation enthalpy of gaseous BaCeO3 (-1065 ± 25 kJ/mol) at 298 K was determined. Energetically favorable structures of gaseous CeO2 and BaCeO3 were found and vibrational frequencies were evaluated in the harmonic approximation.
The stability of BaCeO3 gaseous species was confirmed by high-temperature mass spectrometry. Gas-phase reactions involving gaseous barium and cerium oxides with gaseous barium cerate were studied. The enthalpies of the formation reactions of gaseous barium cerate from gaseous BaO and CeO2 were evaluated theoretically and the obtained values were in agreement with the experimental ones. Copyright © 2016 John Wiley & Sons, Ltd.
已知BaCeO₃物质是优异的质子导体，是氢浓缩器和燃料电池中电解质的潜在候选物。钡和铈的氧化物因其反应活性，会形成气态缔合体——由两种不同类型原子（不包括氧）组成的复杂分子。要预测由钡和铈的氧化物形成气态缔合体的可能性，了解它们的热力学特性很重要。在本研究之前，气态铈酸盐并不为人所知。
采用高温克努森泻流质谱法测定BaO-CeO₂体系上方气相物种的分压，并推导气态CeO₂和BaCeO₃的生成焓。用MS-1301质谱仪进行分压和反应焓的测量。蒸发使用装有研究样品的钼和钨泻流池，并以纯金作为参考物质。通过几种量子化学方法对气态二氧化铈和铈酸钡进行了理论研究：DFT M06、DFT PBE0和MP2。
在1900 - 2120 K温度范围内，发现CeO和CeO₂是固态CeO₂上方的主要气相物种。在BaO-CeO₂混合物上方的气相中发现了Ba、BaO、CeO、CeO₂和BaCeO₃物种。根据气态反应BaO + CeO₂ = BaCeO₃的平衡常数，确定了气态BaCeO₃在298 K时的标准生成焓（-1065 ± 25 kJ/mol）。发现了气态CeO₂和BaCeO₃能量有利的结构，并在简谐近似下评估了振动频率。
高温质谱法证实了BaCeO₃气态物种的稳定性。研究了涉及气态钡和铈的氧化物与气态铈酸钡的气相反应。从气态BaO和CeO₂生成气态铈酸钡的反应焓进行了理论评估，所得值与实验值一致。版权所有© 2016约翰威立父子有限公司。
