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Death and Life of Catalysts: a Theory-Guided Unified Approach for Non-Critical Metal Catalyst Development

Periodic Reporting for period 3 - DeLiCAT (Death and Life of Catalysts: a Theory-Guided Unified Approach for Non-Critical Metal Catalyst Development)

Reporting period: 2019-03-01 to 2020-08-31

Catalysis plays a pivotal role in all strategies towards sustainable chemical technologies of the future. To minimize the adverse effects due to the use of non-renewable hydrocarbon feedstocks, novel technologies have to be conceived and materialized shortly to enable the direct use of renewable feedstocks and to make the existing chemical processes more atom- and energy-efficient. Endeavors towards the sustainable use of feedstocks should be accompanied by the efforts to make the catalyst utilization also more sustainable. The current paradigm is that most developments in catalysis largely rely on empirical findings gained through laborious experimental efforts, in which potentially active systems can be overlooked simply because of the sub-optimal conditions of the initial activity assessment. Mechanistic and kinetic studies could provide a framework for a more adequate assessment of new catalysts, but such rigorous experiments are not practical for general catalyst discovery. Modern chemical theory and computations hold a promise to be employed in new efficient theory-guided approaches for rational catalyst and process development.

The main aim of DeLiCat is to develop an integrated computational and experimental strategy for the design and optimization of efficient catalytic systems based on non-critical metal-based catalysts for sustainable chemical transformations such as catalytic reduction of carbonyl-containing compounds. Besides their fundamental importance to synthetic organic chemistry as the sustainable alternatives to the conventional stoichiometric routes producing vast amounts of waste, these highly atom-efficient catalytic transformations can be employed in various processes ranging from biomass upgrading to hydrogen storage and fine organic synthesis.

The innovative workflow that we develop in the course of this project integrates advanced chemical theory and computational screening with an experimental chemical and chemical engineering approaches in an efficient knowledge exchange loop. An important goal of the theoretical program in this project is to develop new operando modeling approaches that would allow to better understand how variation in the reaction conditions affects the behavior of the catalyst system. These insights would help the experimentalist navigate through the highly complex and multidimensional condition space towards enhanced catalyst lifetime and overall process efficiency.

DeLiCat puts a special emphasis on understanding the undesirable side-reactions resulting in the deactivation of the catalyst and decreasing thus the efficiency of the overall project. Catalyst deactivation is inevitable. However, we propose that by optimizing the catalytic system, one can postpone the deactivation and, hence, improve substantially catalyst performance in terms of the catalyst use so that higher yield of desirable products could be produced with lower catalyst concentration, making the catalyst use more sustainable and contributing to the improved economics of the process. In this project, we use computer simulations to understand the chemistry of the “death” and the “life” of catalyst systems and learn how to control the underlying chemical transformations. These insights are then used in the targeted design of novel multifunctional catalyst systems to direct the selectivity of the reaction network and to prevent deactivation paths.
The cross-disciplinary research efforts in DeLiCat are split into 4 interconnected computational and experimental sub-projects. Sub-project 1 is currently devoted to computational method development. Here we are working on the development of (i) new operando approaches to modeling multicomponent reactive environments, (ii) automated workflow for identification and analysis of reactive ensembles in multifunctional catalytic systems, and (iii) a method for automated accelerated reaction network analysis in multicomponent catalytic systems. The methodologies developed in sub-project 1 are directly used in the computational sub-projects 2 and 3 devoted to the mechanistic analysis of the practical catalytic systems relevant to the objectives of this sub-project, namely, the homogeneous and heterogeneous catalysts for the conversion of carbon-containing substrates and carbon dioxide. In these projects, we employ modern computational chemistry techniques to obtain a deep insight into the “life” and “death” of the relevant catalyst platforms. The experimental sub-project 4 is devoted to (i) the development of new instruments for studying the deactivation phenomena in practical catalytic systems and (ii) to the development of new catalysts systems based on earth-abundant elements (e.g. manganese). The experiments carried out in sub-project 4 provide crucial guidance and validation to the concepts and insights formulated in the accompanying computational projects.

The work carried out so far within the method development sub-project 1 of DeLiCat has been devoted to the development of new approaches for automated prediction and analysis of the reactive sites and conversion paths in homogeneous and heterogeneous catalysis are considered. The research was carried out on model systems developed in the accompanying experimental sun-project 4. So far we have put forward a practical workflow enabling an efficient analysis and assessment of the effect of varying the condition space parameters on the thermodynamics of the competing reaction channels. We propose that this approach can be used for the initial screening of condition-dependencies for practical catalytic systems and to predict the reaction conditions, under which catalyst lifetime can be extended. The ongoing research focuses on the integration of this thermodynamic approach into more detailed kinetic models to enable a comprehensive description of multicomponent reactive solutions. In parallel, we have made great progress in the development of a computational methodology for the automated reaction path analysis and active site determination in the homogeneous and heterogeneous multifunctional catalyst system. The software for such an analysis is currently being tested and the computational predictions are being validated by dedicated experimental studies. In the next period, after the software has been optimized and validated, it will be used to expand the scope of the mechanistic computational sub-projects 2 and 3.

The computational sub-projects 2 and 3 are devoted to the detailed mechanistic analysis of the fundamental factors that control the behavior of the selected homogeneous and heterogeneous catalytic systems for the selective reduction of oxygenated compounds, e.g. carbonyl-containing substrates and CO2. So far, a detailed mechanistic analysis of the behavior of bidentate Mn(I)-based homogeneous catalysts towards ester and ketone reduction, discovered in the experimental part of the project, has been carried out. Using the thermodynamic analysis approach developed in sub-project 1, a deep insight into the condition-dependencies of a new Mn(I)-P,N ester reduction system have been put forward. Computations have been carried out to explain the differences in the catalytic reactivity of Mn(I)-based bidentate ligands. Future work will target the development of comprehensive kinetic models for these systems to pin-point the critical parameters limiting their practical applicability. The computational work within sub-project 2 has been so far devoted to the mechanistic studies on the conversion of carbon dioxide, a prominent greenhouse gas, to liquid fuels over multifunctional heterogeneous catalysts. The results obtained point to the crucial role of active site cooperativity and suggest important design rules for the improved catalytic systems. The insights obtained so far lay the ground for further computational research aimed at discovering new reaction channels for the utilization of carbon dioxide wastes for the production of higher-value chemical products.

The experimental part of DeLiCat, sub-project 4, develops along two main lines, namely, (i) the method development for the detailed kinetic analysis of complex chemical conversions and (ii) the synthesis and investigation of new Mn-based catalytic systems for the reduction fo carbonyl-containing organic substrates. During the previous project period, main efforts have been put in establishing the dedicated experimental infrastructure and developing a fast and reliable methodology for in-depth kinetic studies of catalytic reaction mixtures. The experimental work carried out so far has resulted in the synthesis of a series of new bidentate Mn(I) catalysts showing a divergent reactivity towards different carbonyl-containing substrates and reduction approaches. Their catalytic behavior has been investigated in detail. The understanding of these new catalysts obtained from both the experimental and computational studies will be used at the next project phase to develop more stable and active catalytic systems. Here we will simultaneously target both the development of new Mn-based catalysts and the optimization of their use in the actual catalytic process.
DeLiCat project has already delivered several important experimental and theoretical results that can be regarded as being well beyond the state-of-the-art.
- We have developed a new approach to computationally analyzing the effect of the reaction conditions on the behavior of complex reactive solutions such as the catalytic mixtures investigated in this project. The practical implementation of the theoretical methodology has been carried out in collaboration with researchers from ITMO University, Russia. This approach allows screening the vast condition space and pin-point the conditions, under which the catalyst would be less susceptible to deactivation, while the catalytic reaction itself is still possible. The next step is to combine this approach with a microkinetic model to enable a comprehensive description of realistic catalytic systems. As a result, we will obtain a practical computational model that could be used for the full ab initio optimization of a practical catalytic system.
- In collaboration with other researchers at TU Delft, an advanced sampling system has been developed allowing for a high-resolution kinetic investigation of complex reactive systems. The developed instrument allows a detailed investigation of the reactions operating under extreme conditions, which are very difficult to carry out using conventional techniques. This system will play a crucial role in the experimental studies carried out at the next phase of the project.
- Novel synthetic methodologies towards various hetero-donor N-heterocycle carbene-based bidentate and pincer Mn-based catalysts have been developed so far. We were able to identify catalytic materials based on the earth-abundant manganese metal outperforming the available literature examples and showing catalytic performance comparable to that secured for the more scarce and expensive noble metal catalysts. We anticipate that further studies will provide more detailed information on the reaction pathways underlying the catalytic behavior of Mn-based catalysts under the catalytic reduction conditions and guide the development of more active and stable catalytic systems.
- A new accelerated reaction network analysis method has been developed that outperforms the currently available approaches. Specifically, our methodology allows us to directly sample rare-events and extended reaction networks involving multimolecular reactions in multicomponent catalytic systems. Further research is required to validate and optimize this methodology. We expect that this methodology will play a key role in guiding the experimental and computational mechanistic efforts in their search for the convoluted reaction networks underlying the behavior of the realistic catalytic systems investigated in this project.