Remote detection NMR imaging of gas phase hydrogenation in microfluidic chips

Abstract

The heterogeneous hydrogenation reaction of propene into propane in microreactors is studied by remote detection (RD) nuclear magnetic resonance (NMR). The reactors consist of 36 parallel microchannels (50 × 50 μm(2) cross sections) coated with a platinum catalyst. We show that RD NMR is capable of monitoring reactions with sub-millimeter spatial resolution over a field-of-view of 30 × 8 mm(2) with a steady-state time-of-flight time resolution in the tens of milliseconds range. The method enables the visualization of active zones in the reactors, and time-of-flight is used to image the flow velocity variations inside the reactor. The overall reaction yields determined by NMR varied from 10% to 50%, depending on the flow rate, temperature and length of the reaction channels. The reaction yield was highest for the channels with the lowest flow velocity. Propane T1 relaxation time in the channels, estimated by means of RD NMR images, was 270 ± 18 ms. No parahydrogen-induced polarization (PHIP) was observed in experiments carried out using parahydrogen-enriched H2, indicating fast spreading of the hydrogen atoms on the sputtered Pt surface. In spite of the low concentration of gases, RD NMR made imaging of gas phase hydrogenation of propene in microreactors feasible, and it is a highly versatile method for characterizing on-chip chemical reactions.

Efficient Catalytic Microreactors with Atomic‐Layer‐Deposited Platinum Nanoparticles on Oxide Support

“…Consequently,t he spins at the exit (bottom)o ft he reactora re observed first and those at the entrance (top) last. [45],a nd the resultingv alue was 600 AE 90 ms. The arrow becomes slightly elongated at longerT OF instances, implyingt hat the flow velocity is slightly smaller in the outer- Figure 5t he right most panel), the signal amplitude is considerably higher in the lower parto ft he chip than in the upperp artd ue to T 1 relaxation.…”

“…The sensitivity problem is especially difficult when low density gaseous fluids are investigated. [45] The method provides also time-of-flight (TOF)i nformation as the travel time from the encoding region to the detector depends on the initial spatialp osition of the encoded molecule. [36][37][38][39][40][41][42] In this work, the yield of the hydrogenation reaction in the microfluidic chips was determined from 1 HNMR spectra measured by an ultrasensitive microsolenoidw ound around an outlet capillaryw hile the gas mixture was flowing out from the reactor.F urthermore, remote detection (RD) NMR [43,44] was utilized for visualization of the gas flow in the reactors.…”

“…[36][37][38][39][40][41][42] In this work, the yield of the hydrogenation reaction in the microfluidic chips was determined from 1 HNMR spectra measured by an ultrasensitive microsolenoidw ound around an outlet capillaryw hile the gas mixture was flowing out from the reactor.F urthermore, remote detection (RD) NMR [43,44] was utilized for visualization of the gas flow in the reactors. [39,45,48] Now the state-of-the-art NMR techniquesa re exploited in the characterization of novel, efficient, ALD coated microreactors. RD has been shown to provide an 800-fold sensitivity boost as compared to ac orresponding experiment carried out by the large coil around the reactor.…”

NMR imaging of gas phase hydrogenation in a packed bed flow reactor

“…Furthermore, a method using the temperature dependence of chemical shift difference between the two signals of ethylene glycol, well known from high resolution NMR spectroscopy [26], was adapted for temperature measurements within an NMR compatible reactor [27]. Even gas phase reactions were investigated by using hyperpolarization or remote detection techniques [28][29][30].…”

NMR Hyperpolarization Techniques of Gases

“…Further efforts were directed to the development of the concept by employing micro-engineering technologies to produce micro-structured lab-on-a-chip reactors with the catalyst (sputtered Pt) deposited on the inner surface of the channels. [231] It was found that these reactors did not provide PHIP. However, these studies provided a platform for further development of RD NMR for future HP applications, e.g., by using Hadamard encoding to achieve a better chemical resolution.…”