Rational Design of Noble Metal Catalysts for CO2 hydrogenation and Olefin hydroformylation

Abstract

The advancement of industry and modern civilization has greatly enriched human life, yet it has simultaneously generated a range of serious problems. The continuous release of carbon dioxide (CO2) into the atmosphere has led to the greenhouse effect and related numerous environmental problems, posing a direct threat to the future of humanity. Addressing this problem is no longer optional but an essential, pressing responsibility that requires proactive and sustainable solutions. However, petroleum- derived chemical products remain indispensable in supporting the foundations of modern life, making it unrealistic to eliminate them abruptly. Therefore, establishing a sustainable carbon cycle is essential for reducing carbon emissions and ultimately achieving net carbon reduction. This dissertation focuses on presenting a roadmap for producing high-value chemicals from CO2. Specifically, it proposes a two- step approach: the conversion of CO2 to CO (carbon monoxide), followed by the synthesis of industrially important aldehydes from the produced CO. Realizing this strategy requires achieving high conversion efficiency under low energy input, which in turn highlights the essential role of catalyst development. In Chapter 2, this part develops platinum-based single atom catalysts for the reverse water gas shift reaction, a key carbon utilization pathway that converts CO2 to CO. Due to an endothermic reaction, high temperature is typically required, but operating at relatively low temperature is particularly challenging. To address this limitation, this chapter introduces aluminum into a platinum-ceria catalyst to improve carbon monoxide formation under mild reaction conditions. The synthesized Pt–Al/CeO2 catalyst exhibits a maximum CO formation rate of 33,400 molCO molpt −1min−1 at 400 oC, corresponding to a 43% enhancement relative to Pt/CeO2 catalyst. Mechanistic analysis using in situ DRIFTS shows that Al incorporation modifies the surface intermediates involved in CO2 conversion. Ambient pressure x-ray photoelectron spectroscopy further reveals that the Al incorporated catalyst maintains a higher Ce3+ fraction during the reaction, enabling more efficient CO2 activation. This study demonstrates that controlling surface intermediates can significantly enhance the reverse water gas shift activity and provides guidance for designing catalysts that operate efficiently at lower temperatures. In Chapter 3, this part addresses the long-standing gap between homogeneous and heterogeneous catalysis by establishing an electronically guided design framework for RhP nanoparticles. Using the d-band center as a useful descriptor, the electronic properties of heterogeneous Rh–P phases are aligned with those of well-defined homogeneous Rh metal ligand complexes. Machine learning accelerated molecular dynamics and density functional theory are used to screen a compositional library of Rh–P systems, revealing a strong relationship between d-band center deviation and hydroformylation activity. Experimental validation confirms that the Rh3P composition, predicted as optimal by electronic structure matching, delivers a reaction rate of 13,357 h−1, a 25% enhancement over the state of the art RhP nanoparticle catalyst. By demonstrating how homogeneous catalytic insights can be translated into the design of heterogeneous catalysts, this chapter establishes a broadly applicable electronic structure- guided catalyst development strategy. In Chapter 4, this study investigates how the electron density of Rh can be tailored by controlling the amount of CeO2 within CeO2-Al2O3 mixed oxide supports. It is demonstrated that atomically dispersed Rh species can be formed on these supports and that the resulting electron density depends sensitively on the ceria content. The optimized Rh/CeO2-Al2O3 catalyst exhibits propylene hydroformylation activity comparable to that of the homogeneous , Wilkinson catalyst, RhCl(PPh3)3. Combined analysis and theoretical modeling show that an increased Ce3+ fraction enhances the electron density of Rh, weakens CO adsorption, and ultimately promotes the hydroformylation activity. Furthermore, the catalyst enables selective aldehyde formation from a mixed C2 to C4 olefin/paraffin gas, illustrating practical separability and high value conversion. This study highlights that heterogeneous catalysts can be efficiently designed to mimic the performance of homogeneous catalysts by controlling the local coordination environment and electronic structure of metal species. In Chapter 5, this chapter presents a layered titanate structure platform that enables direct insertion of desired metal cations without structural deformation. When the layered titanate structure is used as a catalyst support, alkali metal intercalation precisely tunes the charge density of supported Rh species. Among the catalysts with various intercalated alkali ions in the interlayer position, Rh/K-LT catalyst exhibits a turnover frequency of 23,685 h−1 in propylene hydroformylation, outperforming previously reported Rh-based homogeneous catalysts. Combined in situ and ex situ characterization with density functional theory reveals that alkali metal intercalation enhances charge transfer to Rh atoms, improving adsorption behavior and catalytic activity. This chapter establishes a wide cation intercalation platform and provides a general strategy for charge modulation in layered titanates, enabling rational catalyst design across diverse reactions. In Chapter 6, this content introduces a cation exchange strategy to prepare Rh single atom catalysts anchored in an anatase TiO2 lattice. By substituting surface Ti with Rh atoms, abundant oxygen vacancies are generated to stabilize isolated metal atoms and increase their electron density. Comprehensive characterization shows that these Rh/TiO2 single atom catalysts possess outstanding redox flexibility, resistance to sintering, and strong H2 spillover capabilities. These features promote the formation of RhH(CO)2 hydride intermediates, which serve as key reactive species in hydroformylation. As a result, the catalyst achieves a turnover frequency of 34,364 h−1 in propylene hydroformylation, surpassing even the benchmark homogeneous Wilkinson catalyst. The system also demonstrates broad substrate applicability to ethylene and butylene, highlighting its industrial promise and establishing a new performance benchmark for single atom hydroformylation catalysts. In Chapter 7, this study systematically compares the catalytic behavior of Rh single atom catalyst, cluster catalysts, and nanoparticle catalyst for olefin hydroformylation. In situ spectroscopies and theoretical investigations reveal that Rh cluster catalyst possesses intermediate chemical and electronic characteristics between a Rh single atom and a metallic nanoparticle. This unique configuration enables the Rh cluster to achieve a turnover frequency of about 25,589 h−1, which is five times higher than that of single atom catalyst and nine times higher than that of nanoparticle catalysts. Density functional theory-based calculation presents that the Rh cluster catalyst has optimal CO adsorption energies that allow efficient overcoming of the energy barrier associated with the CO insertion step, the rate- determining step in hydroformylation. Density of states and crystalline orbital analyses confirm that the electronic structure of Rh clusters is tuned to an optimal regime with the facilitation formation of hydride species. This chapter highlights the distinctive catalytic advantages of cluster-based catalysts and offers mechanistic insight for designing next-generation high-performance hydroformylation catalysts.