GREEN CHEMISTRY
Lastly , various reducing agents were tested to evaluate their influence on the hydrogenation activity and palladium distribution . Finding the right reducing agent and reduction procedure is crucial to not only ensure complete reduction of the noble metal but also to prevent agglomeration of the active phase . Reducing agent A led to a slightly lower activity in crotonic acid conversion , whereas using reducing agent B led to a 15 % increase in nitrobenzene conversion .
Comparisons of results
Beside the previously discussed palladium-containing catalysts , platinum-coated microsphere catalysts were prepared using an analogous , optimised synthesis route . Both metals are highly catalytically active in hydrogenation reactions .
There were differences in their respective performances , with platinum microspheres displaying higher activity for nitrobenzene hydrogenation and palladium microspheres showing higher activity for crotonic acid hydrogenation . This trend is similar to the behaviour of our standard carbon powdersupported catalysts .
To compare the novel microsphere catalysts with conventional powder catalysts , two catalysts with the same precious metal loading ( 1 wt % platinum ) were prepared using carbon powder as well as a microsphere carrier . With a BET surface area of 1,230 and 1,330 m 2 / g , the surface area for both types is quite similar .
By using platinum-loaded microspheres catalysts an improvement in hydrogenation reactivity for both test reactions was achieved . ( Figure 4 ) We believe that a smaller particle size of the active
phase on the catalyst surface is the reason for the improved conversion rate with the microsphere catalysts . Further investigations to prove this hypothesis are ongoing .
Conclusion
This investigation presented the successful development of platinumand palladium-loaded catalysts using carbon microsphere supports . By optimising the preparation method , a significant increase in the hydrogenation activity of nitrobenzene and crotonic acid was achieved . Furthermore , it was ensured that the precious metal remains homogeneous distributed on the microspheres surface .
The use of carbon microspheres offers many advantages , including high specific BET surface areas of up to 1,200 m 2 / g and beneficial properties such as mechanically robust , low pressure drop and easy filtration behaviour .
Figure 4 - Comparison of hydrogenation activity of 1 % Pt-based microspheres & powder catalysts
The platinum and palladium microspheres catalysts show promising results and they can be produced with particle sizes of 200 and 470 µ m . By combining these properties , precious metal-based microsphere catalysts have the potential to bridge the gap between batch and continuous production processes in fine chemical and pharmaceutical applications .
Based on this work , new opportunities for catalyst design and application in both batch and continuous systems are emerging . Further research and optimisation of microsphere catalysts will be focused on expanding the portfolio in order to transfer the improvements to other applications and catalyst systems . One such ongoing project is the development of analogous ruthenium-coated microsphere catalysts . ●
References : 1 : M . Poliakoff & P . Licence , Nature , 2007 , 450 , 810 2 : O . Deutschmann , H . Knözinger , K . Kochloefl & T . Turek , Ullmann ’ s Encyclopedia of Industrial Chemistry ( Heterogeneous Catalysis & Solid Catalysts ), Wiley-VCH Verlag , Weinheim , 2000 3 : B . Kamm , P . R . Gruber & M . Kamm , Ullmann ’ s Encyclopedia of Industrial Chemistry ( Biorefineries - Industrial Processes & Products ), Wiley-VCH Verlag , Weinheim , 2016 4 : A . R . Bogdan & A . W . Dombrowski , J . Med . Chem ., 2019 , 62 , 6422
Artur Gantarev
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