Final Report Summary - TCPBRCBDP (Tandem catalysis for the production of biofuel-related chemicals from biomass-derived polyols)
The main objective of the present project is to develop a novel one pot process for polyol conversion into valuable acetals via tandem Fischer-Tropsch (F-T) hydroformylation and acetalisation reactions. Acetalisation could be a thermal induced automatic reaction whereas the first two transformations require nanoparticle (NP) catalyst and homogenous catalyst, respectively. One of the main goals of this project is therefore to develop stable, active hybrid catalyst comprising NP catalyst and homogenous catalyst to promote the two reactions simultaneously. The performance of the catalyst will be subsequently evaluated and the fate of the catalyst during reaction will be analysed by advanced in situ spectroscopic techniques.
Since the beginning of the project, we have conducted research work in consecutive six phases, guided by the grant agreement form including:
(1) synthesis of more stable metal NP catalyst;
(2) synthesis of active Rh complexes;
(3) synthesis of hybrid Ru NP-Rh complex catalyst;
(4) separate F-T and hydroformylation reaction tests and parameter optimisation;
(5) tandem F-T - hydroformylation reaction and F-T - hydroformylation-acetalisation reaction over the hybrid catalyst; and
(6) in situ spectroscopic investigation of the catalyst.
In the first phase, we successfully prepared two types of new NP stabilisers based on the modification of poly-vinyl-pyrrolidone (PVP). One is the alkyl chain modified PVP and the other type is the carboxylate modified PVP. In particular, the carboxylate functionalised PVP combines steric, coordinative and electrostatic properties to provide enhanced stabilisation of the metal NPs, when compared with unfunctionalised PVP. Ru NPs were readily synthesised in water or ethylene glycol using H2 or NaBH4 as reductant that were stable upon storage for at least one year, and were also active and stable in model catalytic reactions.
The second phase was focused on the preparation of HRh(CO)(TPPTS)3 for the hydroformylation reaction. This complex was well developed previously. We repeated its synthesis, with a major purpose to be familiar with classical hydroformylation catalyst, and to use it as a benchmark for the hydroformylation reaction. Following that, we analysed the Ru NP catalysed F-T reaction and HRh(CO)(TPPTS)3 catalysed hydroformylation reaction separately (phase 3), to understand the performance-parameter relationship for each reaction. As such, the optimised (compromised) reaction condition for tandem F-T and hydroformylation reaction was identified.
The essence of the success of the hybrid catalysts is to find a support/stabiliser that could sustain both a NP and a mononuclear complex. We synthesised a new polymer that bears moieties for NP stabilisation (based on pyrrolidone groups) and moieties for coordination with metal centers (based on tri-phenyl phosphine groups) to support both Ru NPs and Rh complex. Rhodium is firstly coordinated to the copolymers, following a classic route for the HRh(CO)(TPPTS)3 synthesis and then Ru NPs were made in-situ from RuCl3 by NaBH4 reduction. Under transmission electron microscopy (TEM) the presence Ru NPs is evident and 31P NMR suggests the coordinating between P and Rh. These highlighted that the hybrid Ru-Rh catalysts were successfully prepared.
Afterwards the combined F-T and hydroformylation reaction were carried out in the presence of the hybrid Ru-Rh catalyst. Exactly as expected in the proposal, the incorporation of Rh into the catalytic system increased the aldehyde and alcohol yield from 15 to 22 % at 130 degrees of Celsius, and from 4 to 12 % at 150 degrees of Celsius. Interestingly, at 150 degrees of Celsius, the activity of Ru-Rh hybrid catalyst was even higher than Ru NPs alone, suggesting a synergetic effect of Rh on the CO activation. Finally, the Ru-Rh hybrid catalyst was tested for syngas conversion in ethylene glycol to achieve to produce acetals / ketals directly from polyols and syn-gas via tandem F-T, hydroformylation and acetalisation reactions. Under optimised conditions, we can achieve a dioxane (desired product after the three-step tandem reaction) yield of more than 50 wt %, demonstrating the feasibility of the proposed strategy for the one-pot synthesis of acetals from polyol and syngas over Ru-Rh hybrid catalyst.
The catalyst deactivates upon recycling. This is due to the formation of Rh NPs which is much less active in the hydroformylation reaction. Therefore we applied in-situ X-ray absorption spectroscopy (XAS) to investigate the formation of Rh NPs from Rh mononuclear species. A model system, RhCl3 dissolved in ethylene glycol in the presence of additives (ligands, surfactants, etc.) at elevated temperature, was studies by in-situ XAS. A four stage process for the transformation of RhCl3 into Rh NPs was revealed and the detailed chemical events at each stage were identified. This part of study does not only provide clues to prevent NP formation when undesired (such in our case) and also helps to better control NP synthesis for certain applications.
To summarise, we have achieved the major objectives outlined in the project. Tandem F-T, hydroformylation and acetalisation reaction can occur in a step wise manner over tailor-made hybrid catalyst, leading to one pot synthesis of acetals from polyols and syngas. This might provide a novel way for the green acetal manufacturing. Furthermore, our work is likely to inspire more research on designing multifunctional catalyst for the one-pot synthesis of green chemicals from renewable resources.
Since the beginning of the project, we have conducted research work in consecutive six phases, guided by the grant agreement form including:
(1) synthesis of more stable metal NP catalyst;
(2) synthesis of active Rh complexes;
(3) synthesis of hybrid Ru NP-Rh complex catalyst;
(4) separate F-T and hydroformylation reaction tests and parameter optimisation;
(5) tandem F-T - hydroformylation reaction and F-T - hydroformylation-acetalisation reaction over the hybrid catalyst; and
(6) in situ spectroscopic investigation of the catalyst.
In the first phase, we successfully prepared two types of new NP stabilisers based on the modification of poly-vinyl-pyrrolidone (PVP). One is the alkyl chain modified PVP and the other type is the carboxylate modified PVP. In particular, the carboxylate functionalised PVP combines steric, coordinative and electrostatic properties to provide enhanced stabilisation of the metal NPs, when compared with unfunctionalised PVP. Ru NPs were readily synthesised in water or ethylene glycol using H2 or NaBH4 as reductant that were stable upon storage for at least one year, and were also active and stable in model catalytic reactions.
The second phase was focused on the preparation of HRh(CO)(TPPTS)3 for the hydroformylation reaction. This complex was well developed previously. We repeated its synthesis, with a major purpose to be familiar with classical hydroformylation catalyst, and to use it as a benchmark for the hydroformylation reaction. Following that, we analysed the Ru NP catalysed F-T reaction and HRh(CO)(TPPTS)3 catalysed hydroformylation reaction separately (phase 3), to understand the performance-parameter relationship for each reaction. As such, the optimised (compromised) reaction condition for tandem F-T and hydroformylation reaction was identified.
The essence of the success of the hybrid catalysts is to find a support/stabiliser that could sustain both a NP and a mononuclear complex. We synthesised a new polymer that bears moieties for NP stabilisation (based on pyrrolidone groups) and moieties for coordination with metal centers (based on tri-phenyl phosphine groups) to support both Ru NPs and Rh complex. Rhodium is firstly coordinated to the copolymers, following a classic route for the HRh(CO)(TPPTS)3 synthesis and then Ru NPs were made in-situ from RuCl3 by NaBH4 reduction. Under transmission electron microscopy (TEM) the presence Ru NPs is evident and 31P NMR suggests the coordinating between P and Rh. These highlighted that the hybrid Ru-Rh catalysts were successfully prepared.
Afterwards the combined F-T and hydroformylation reaction were carried out in the presence of the hybrid Ru-Rh catalyst. Exactly as expected in the proposal, the incorporation of Rh into the catalytic system increased the aldehyde and alcohol yield from 15 to 22 % at 130 degrees of Celsius, and from 4 to 12 % at 150 degrees of Celsius. Interestingly, at 150 degrees of Celsius, the activity of Ru-Rh hybrid catalyst was even higher than Ru NPs alone, suggesting a synergetic effect of Rh on the CO activation. Finally, the Ru-Rh hybrid catalyst was tested for syngas conversion in ethylene glycol to achieve to produce acetals / ketals directly from polyols and syn-gas via tandem F-T, hydroformylation and acetalisation reactions. Under optimised conditions, we can achieve a dioxane (desired product after the three-step tandem reaction) yield of more than 50 wt %, demonstrating the feasibility of the proposed strategy for the one-pot synthesis of acetals from polyol and syngas over Ru-Rh hybrid catalyst.
The catalyst deactivates upon recycling. This is due to the formation of Rh NPs which is much less active in the hydroformylation reaction. Therefore we applied in-situ X-ray absorption spectroscopy (XAS) to investigate the formation of Rh NPs from Rh mononuclear species. A model system, RhCl3 dissolved in ethylene glycol in the presence of additives (ligands, surfactants, etc.) at elevated temperature, was studies by in-situ XAS. A four stage process for the transformation of RhCl3 into Rh NPs was revealed and the detailed chemical events at each stage were identified. This part of study does not only provide clues to prevent NP formation when undesired (such in our case) and also helps to better control NP synthesis for certain applications.
To summarise, we have achieved the major objectives outlined in the project. Tandem F-T, hydroformylation and acetalisation reaction can occur in a step wise manner over tailor-made hybrid catalyst, leading to one pot synthesis of acetals from polyols and syngas. This might provide a novel way for the green acetal manufacturing. Furthermore, our work is likely to inspire more research on designing multifunctional catalyst for the one-pot synthesis of green chemicals from renewable resources.