In Situ Infrared Spectroscopy as a Tool for Monitoring Molecular Catalyst for Hydroformylation in Continuous Processes

Abstract

Non-invasive in situ monitoring of catalyzed chemical reactions can show and probe the stability of the catalyst and ensure a high yield of the desired chemical processes. Infrared in situ measurement techniques in attenuated total reflection (ATR) and transmission mode were used to assess the feasibility of these methods and ultimately compare their ability to monitor and detect active or degrading catalyst species. Four different process configurations were used, namely (i) a stirred tank reactor equipped with ATR-IR; (ii) a continuously operated miniplant with ATR-IR; (iii) a continuously operated miniplant with transmission-IR; (iv) a stirred tank reactor equipped with transmission-IR. The established hydroformylation of a long-chain olefin catalyzed by a rhodium-phosphite catalyst was taken as a representative reaction. The potential for process monitoring in molecular catalysis was evaluated. Advanced chemometric analyses by Band Target Entropy Minimization (BTEM) were performed following spectral monitoring to obtain pure component spectra estimates as well as relative time-dependent concentration profiles. In general, this study showed that infrared measurements in transmission mode are able to detect active catalytic species and can follow deactivation phenomena in batch reactions and continuously operated miniplants. Apart from the substrates and products, a number of catalytic intermediates appear to be in equilibrium exchange at reaction conditions and hence the deconvolution of multispecies spectra exhibits superimpositions of these species. Quantum chemical calculations support the structural identification of measured vibrational spectra. This comparative study of ATR versus transmission and batch experiment versus continuously operated miniplant shows that transmission IR is capable of getting in-depth spectroscopic data that can be deconvoluted by BTEM. A distinct dosing strategy is important to get meaningful data on the molecular catalyst under process conditions. This study gives a unique perspective on in situ spectroscopic infrared investigations in molecular catalysis and future process control.

Multi-nuclear, high-pressure, operando FlowNMR spectroscopic study of Rh/PPh3 – catalysed hydroformylation of 1-hexene

“…Van Leeuwen, Kamer and co-workers have developed bespoke high-pressure Infrared spectroscopy (HP-IR) autoclaves that allow operando IR studies of fast catalytic reactions under realistic conditions, 23 and other groups have used similar setups to follow Rh-catalysed hydroformylation on different scales. 29,30 IR spectroscopy offers high sensitivity and fast measurements compared to NMR spectroscopy, but it requires calibration to be quantitative and provides limited structural information on the intermediates observed. 31 On-line high resolution FlowNMR spectroscopy has recently been shown to be a powerful operando reaction monitoring technique for homogeneous catalytic systems under realistic conditions due to its quantitative nature and high specificity in complex reaction mixtures.…”

Synthesis of High Metal Loading Single Atom Catalysts and Exploration of the Active Center Structure

“…With appropriate probe molecules, FTIR spectroscopy is employed to confirm the presence of SACs and even quantify the dispersed SACs. The advantages of FTIR spectroscopy include quantification and in situ monitoring [176] . Combined with AC−HAADF−STEM, XAS, and DFT, FTIR offers a powerful toolbox for SACs study.…”

“…The advantages of FTIR spectroscopy include quantification and in situ monitoring. [176] Combined with ACÀ HAADFÀ STEM, XAS, and DFT, FTIR offers a powerful toolbox for SACs study.…”

Design and Use of a High‐Pressure Stirred IR Cell for Operando Studies in Homogeneous Catalysis

“…Although excellent results have been obtained in some cases, [8][9][10][11] the disadvantage of the former class is that the recirculation of the solution can give rise to pressure drops or bubble formation, resulting in a recorded spectrum that is not truly representative of the conditions inside the autoclave. Even a fast consumption of a reacting gas (CO and/or H 2 ) after the solution has left the stirred autoclave can cause the same problem.…”

“…The physical principle on which these systems operate is that of ATR and the limit is the small penetration depth of the signal into the solution resulting in a low sensitivity and a relatively bad signal-to-noise ratio. [4,11] Additionally, the material of the probe material can also be a concern. The two materials employed in the commercially available probes are silicon and diamond.…”