Reactive organic fluid–mineral interactions at elevated temperatures contribute to the evolution of planetary matter. One of the less studied but important transformations in this regard involves the reactions of formic acid with naturally occurring clays such as sodium montmorillonite. To advance a mechanistic understanding of these interactions, we use ReaxFF reactive molecular dynamics (MD) simulations in conjunction with infrared (IR) spectroscopy and X-ray scattering experiments to investigate the speciation behavior of water–formic acid mixtures on sodium montmorillonite interfaces at 473 K and 1 atm. Using a newly developed reactive force field, we show that the experimental IR spectra of unreacted and reacted mixtures can be accurately reproduced by ReaxFF/MD. We further benchmark the simulation predictions of sodium carbonate and bicarbonate formation in the clay interlayers using small-angle and wide-angle X-ray xcattering measurements. Subsequently, leveraging the benchmarked force field, we interrogate the pathway of speciation reactions with emphasis on carbonate, formate, and hydroxide groups, elucidating the energetics, transition states, intermediates, and preferred products. We also delineate the differences in reactivities and catalytic effects of clay edges, facets, and interlayers owing to their local chemical environments, which have far reaching consequences in their speciation behavior. The experimental and simulation approaches described in this study and the transferable force fields can be applied translationally to advance the science of clay–fluid interactions for several applications including subsurface fluid storage and recovery and clay–pollutant dynamics.

中文翻译：

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Na蒙脱石与200°C的水和甲酸相互作用时产生的界面反应性和形态：反应分子动力学模拟，红外光谱和X射线散射测量的见解

高温下反应性有机流体与矿物的相互作用有助于行星物质的演化。在这方面，研究较少但重要的转化之一涉及甲酸与天然粘土如蒙脱土钠的反应。为了提高对这些相互作用的机械理解，我们将ReaxFF反应分子动力学（MD）模拟与红外（IR）光谱和X射线散射实验结合使用，以研究水-甲酸混合物在473蒙脱土钠界面上的形成行为。 K和1个大气压。使用新开发的反作用力场，我们表明ReaxFF / MD可以准确地再现未反应和反应混合物的实验IR光谱。我们进一步使用小角度和广角X射线x散射测量法对粘土夹层中碳酸钠和碳酸氢盐形成的模拟预测进行基准测试。随后，利用基准力场，我们探讨了物种形成反应的途径，重点是碳酸盐，甲酸盐和氢氧化物基团，阐明了能量，过渡态，中间体和优选产物。我们还描述了由于其局部化学环境而导致的粘土边缘，小面和中间层的反应性和催化效果的差异，这对其物种形成行为产生了深远的影响。