Collaborative Research: Combining Operando Spectroscopy and Multi-Scale Modeling to Elucidate the Mechanism of Aqueous Phase Reforming of Oxygenates

面对石油储量的减少和对可持续性的日益需要，社会面临的最大挑战之一是为不断增加的人口提供能源。一种很有希望的策略是从生物质中获取能源。具体地说，据估计，到2030年，美国每年可以生产超过10亿公吨的干生物质，如果转化为可用燃料，其含能量将相当于当前石油消费量的46%。然而，许多将生物质转化为燃料和化学品的过程需要添加氢气。不幸的是，目前从可再生资源中供应氢气的方法效率低、成本高，阻碍了生物质经济的发展。生物质水相重整制氢是一种很有前途的制氢方法。具体地说，在APR中，一部分生物质在催化剂上转化为氢气，催化剂是一种能够在不消耗自身的情况下进行化学反应的材料。尽管前景看好，但到目前为止，APR的氢产率一直令人失望，这表明需要提高APR催化剂的效率。设计新催化剂的第一步需要了解现有催化剂的功能。在这里，克莱姆森大学的雷切尔·盖特曼博士和佐治亚理工学院的卡斯滕·西弗斯博士正在结合最先进的建模和光谱分析，研究APR反应的三个关键步骤：i)氢的去除；ii)一氧化碳的生成；iii)水和一氧化碳生成氢和二氧化碳的反应。由于APR产生的二氧化碳将用于种植新的生物质，因此APR是一个“碳中和”过程。更广泛的影响包括让本科生，特别是妇女和代表性不足的少数群体，参与基础化学和应用化学的有意义的探索。研究成果也在佐治亚州亚特兰大的罗伯特·C·威廉姆斯造纸博物馆展出。在化学系化学催化计划的资助下，克莱姆森大学的雷切尔·盖特曼博士和佐治亚理工学院的卡斯滕·西弗斯博士将多尺度建模和操作光谱分析相结合，提供了关于负载型铂催化剂上生物质衍生氧酸盐水相重整(APR)的活性中心和机理的基本见解。具体地说，该项目侧重于水作为溶剂、共吸附的水和旁观者物种以及载体的性质如何影响选择性和非选择性脱氢、脱羰化和水煤气变换(WGS)。这一新见解将使研究人员能够设计改进的催化剂并优化工艺条件。模拟研究包括将密度泛函理论中的方法与经典分子动力学相结合，以便同时考虑化学键的断裂和形成以及液体水分子在溶剂中的热运动。主要的实验技术是衰减全反射红外光谱，它允许探测浸泡在反应物溶液中的催化剂上的表面物种。实验和理论工作是高度整合的。例如，计算和测量的表面物种的振动频率以及它们形成和转化的速率常数被比较，从而能够开发出与实验观察相一致的模型。私人投资机构大力支持女学生和代表性不足的少数族裔学生参加。此外，该项目的成果通过在佐治亚州亚特兰大的罗伯特·C·威廉姆斯造纸博物馆的展示以及通过生物精炼选举向更广泛的观众展示。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

One of the greatest challenges facing society is supplying energy to an ever-increasing population in the face of declining petroleum reserves and an increasingly need for sustainability. One promising strategy is to derive energy from biomass. Specifically, it is estimated that by 2030, the U.S. can produce more than 1 billion metric tons of dry biomass per year, which would have an energy content equivalent to 46% of the current oil consumption, if properly converted into usable fuels. However, many processes for converting biomass into fuels and chemicals require the addition of hydrogen gas. Unfortunately, present methods for supplying hydrogen gas from renewable resources are inefficient and costly, impeding the expansion of the biomass economy. The aqueous phase reforming (APR) of biomass is a promising strategy for producing hydrogen gas. Specifically, in APR, a part of the biomass is converted into H2 over a catalyst, which is a material that enables a chemical reaction without being consumed itself. Although promising, hydrogen yields from APR have thus far been disappointing, indicating a need to improve the efficiencies of APR catalysts. The first step in designing new catalysts entails understanding the function of the existing catalysts. Here, Dr. Rachel Getman of Clemson University and Dr. Carsten Sievers of the Georgia Institute of Technology are combining state-of-the-art modeling and spectroscopy to study the three key steps of the APR reaction: i) the removal of hydrogen; ii) generation of carbon monoxide; and iii) reaction of water and carbon monoxide to form hydrogen and carbon dioxide. Since the carbon dioxide produced in APR will be used to grow new biomass, APR is a "carbon-neutral" process. Broader impacts involve the inclusion of undergraduates, especially women and underrepresented minorities, into meaningful explorations of fundamental and applied chemistry. Research results are also being presented at the Robert C. Williams Paper Museum of Papermaking in Atlanta, GA.With funding from the Chemical Catalysis Program of the Chemistry Division, Dr. Rachel Getman from Clemson University and Dr. Carsten Sievers from the Georgia Institute of Technology are combining multiscale modeling and operando spectroscopy to provide fundamental insight regarding the active sites and mechanism of the Aqueous Phase Reforming (APR) of biomass-derived oxygenates to hydrogen and carbon dioxide over supported Pt catalysts. Specifically, the project is focused on how selective and non-selective dehydrogenation, decarbonylation, and Water Gas Shift (WGS) are affected by water as a solvent, co-adsorbed water and spectator species, and the nature of support. The new insight will enable researchers to design improved catalysts and optimize process conditions. Modeling studies involve combining methods in density functional theory with classical molecular dynamics, in order to simultaneously incorporate the breaking and forming of chemical bonds and the thermal motions of the liquid water molecules in the solvent. The main experimental technique is attenuated total reflection IR spectroscopy, which allows for probing surface species on catalysts that are immersed in a solution of the reactant. Experimental and theoretical efforts are highly integrated. For example, calculated and measured vibrational frequencies of surface species and rate constants for their formation and conversion are compared, enabling the development of models that are consistent with experimental observations. The PIs are strongly supporting the participation of female and underrepresented minority students. Further, the results from this project are presented to a broader audience through a display at the Robert C. Williams Paper Museum of Papermaking in Atlanta, GA as well as through a biorefining elective.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.