King Richard, Idriss Hicham
Department of Chemistry, The University of Auckland, Auckland, New Zealand.
Langmuir. 2009 Apr 21;25(8):4543-55. doi: 10.1021/la803933t.
The reaction of acetone is studied on the surfaces of polycrystalline UO2, prepared by hydrogen reduction of U3O8 at 770 K. The study is conducted by in situ Fourier transform infrared (FTIR) and temperature-programmed desorption (TPD). Acetone adsorption does not fit the simple Langmuir model, and adsorbate-adsorbate interactions are found to be significant. Acetone adsorbs molecularly on UO2 as evidenced by the nuCO of the eta1(O) mode at 1686 cm(-1). Part of acetone is reduced to the isopropoxide species ((CH3)2HC-O-U4+) upon heating (nu(CC), rho(CH3) at 1167 cm(-1) and nu(CO), rho(CH3) at 980 cm(-1)), and upon further heating, acetates (CH3COO(a), (a) for adsorbed) are observed. Detailed TPD studies indicated that the main reaction of acetone on UO2 is the deoxygenation to propene, driven by the oxophilic nature of UO2. Other reactions were also observed to a lesser extent, and these included reductive coupling to 2,3-dimethylbutene and condensation to mesityl oxide. An attempt to extract kinetic parameters from TPD data was conducted. Three models were studied: variation of heating rate, leading edge analysis (Habenschaden-Kuppers method), and complete analysis. The complete analysis provided the most plausible results, in particular, at low coverage. With this method, at nearly zero coverage the activation energy, Ed, for desorption was found to be close to 140 kJ/mol with a prefactor of 10(13) s(-1). Ed dropped sharply with increasing coverage, theta, to ca. 35 kJ/mol at theta=0.15 with a prefactor of 10(11) s(-1). The activation energy for the desorption of acetone on UO2(111) single crystals, at saturation coverage, was previously found to be equal to 65 kJ/mol using the leading edge analysis.
研究了丙酮在770 K下由U₃O₈氢还原制备的多晶UO₂表面上的反应。该研究通过原位傅里叶变换红外光谱（FTIR）和程序升温脱附（TPD）进行。丙酮吸附不符合简单的朗缪尔模型，且发现吸附质-吸附质相互作用显著。丙酮以分子形式吸附在UO₂上，这由1686 cm⁻¹处η₁(O)模式的νCO所证实。加热时部分丙酮被还原为异丙氧基物种（(CH₃)₂HC - O - U⁴⁺）（1167 cm⁻¹处的ν(CC)、ρ(CH₃)以及980 cm⁻¹处的ν(CO)、ρ(CH₃)），进一步加热时会观察到醋酸盐（CH₃COO(a)，(a)表示吸附态）。详细的TPD研究表明，丙酮在UO₂上的主要反应是脱氧生成丙烯，这是由UO₂的亲氧性质驱动的。还观察到了其他程度较小的反应，包括还原偶联生成2,3 - 二甲基丁烯和缩合生成异亚丙基丙酮。尝试从TPD数据中提取动力学参数。研究了三种模型：加热速率变化、前沿分析（哈本沙登 - 库珀斯方法）和完整分析。完整分析提供了最合理的结果，特别是在低覆盖度时。用这种方法，在几乎零覆盖度下，脱附的活化能Ed接近140 kJ/mol，指前因子为10¹³ s⁻¹。随着覆盖度θ增加，Ed急剧下降，在θ = 0.15时约为35 kJ/mol，指前因子为10¹¹ s⁻¹。先前使用前沿分析发现在饱和覆盖度下，丙酮在UO₂(111)单晶上脱附的活化能等于65 kJ/mol。
