Our protocol describes a method to isolate electrochemical hydrogen production from chemical feedstock hydrogenation in a single reactor. We can characterize the amount of hydrogen used in the desired hydrogenation reaction. Electrochemistry is separated from hydrogenation chemistry.
It reduces the chance of side reactions and allows working with more solvents and concentrations than if restricted to the use of an electrolyte. To begin, clean the palladium wafer bar using the cotton cloth dipped in hexane and roll it with a manual roller until the digital meter reads approximately 150 micrometers. Then use an automatic roller to reduce the thickness to 25 micrometers and cut it into pieces of the desired size.
For annealing, load the rolled palladium foils into a muffle furnace under a nitrogen atmosphere. Heat them at 850 to 900 degrees Celsius for 1.5 hours by gradually increasing the temperature from 25 to 900 degrees Celsius at the rate of 60 degrees Celsius per hour. Prepare a cleaning solution by mixing 10 milliliters of nitric acid, 20 milliliters of 30%hydrogen peroxide, and 10 milliliters of deionized water.
Submerge the annealed palladium foils in the cleaning solution for 20 to 30 minutes until the vigorous bubbling subsides or the solution turns yellow. After washing the palladium foils twice with deionized water, rinse with isopropyl alcohol and air dry. Then assemble the reactor using prepared palladium foils.
To prepare the electroplating solution, dissolve palladium chloride into one molar hydrochloric acid. Fill the electrochemical compartment of the reactor with 24 milliliters of the prepared solution leaving the hydrogenation compartment empty. Place a platinum mesh anode and silver chloride reference electrode in the electrochemical compartment.
Connect the electrodes to a potentiostat and apply the potential of 0.2 volts to palladium foil versus silver chloride until a 15C charge passes. After disassembling the reactor, rinse the resulting palladium membrane twice with deionized water and once with isopropyl alcohol. Once dried with air or nitrogen, check for a visible deposition of black palladium on the membrane surface.
To assemble the reactor, sandwich the prepared palladium membrane between two halves of an electrochemical H cell. Place a chemical resistant gasket between the left side of the cell and the palladium membrane. Once an additional gasket is placed on the right side of the cell, use a clip to seal the reactor configuration.
For electrochemical hydrogenation, fill the electrochemical compartment with 24 milliliters of one molar sulfuric acid. Insert a platinum counter electrode into the electrochemical compartment and connect it to the positive terminal of a power supply. Using copper tape, attach the palladium membrane to the negative terminal.
Then apply a galvanostatic current of 250 milliamperes and 3 to 5 voltage across the cell for 15 minutes. After sampling 30 microliters of the reaction solution, add 24 milliliters in the chemical compartment maintaining galvanostatic current. Collect a sample every 15 minutes with a micro pipette.
Dissolve in one milliliter of dichloromethane in GC-MS vial and store it until the reaction is complete. To analyze the samples, load them into the auto sampler tray. Then click on the MassHunter icon to launch the GC-MS software.
Select sequence and then edit sequence to open the sequence editing window. Fill the sample name, vial position, method path, method file, data path, and data file into the chart. Set the sample type to sample and the dilution to 1.
Click on the method followed by edit entire method to adjust the method. Check both method information and instrument acquisition and press OK.Also, verify data acquisition and data analysis are checked. Leave every other field blank and click OK.Set the sample inlet to GC and the injection source to GC ALS.
Ensure the use MS box is checked, the inlet location is set to front, the MS is connected to front and then click OK.Under the inlet tab, set the heater temperature to 250 degrees Celsius, pressure to 7.2 pounds per square inch, and helium flow to 23.1 milliliters per minute. Under the oven tab, set the initial temperature to 50 degrees Celsius with a one minute hold. Set the ramp rate to 25 degrees Celsius per minute.
The temperature to 200 degrees Celsius with a zero minute hold and press OK.Check that all display signals are not selected and click OK.Set the solvent delay to 2.50 minutes and select OK.Ensure the monitor includes GC oven temperature, GC inlet F temperature, GC inlet F pressure, GC column 2 flow calc, MS EM volts, MS MS source, MS MS quad, and click OK.Enter the desired method name to save the method. Click on the sequence followed by run sequence, and then select run sequence to start the sample analysis. Once the sequence is completed, open the MassHunter software and select the file name to view the data.
To identify the product peaks, click spectrum, then library search report, and OK to compare the acquired mass spectra with the NIST database. Calculate the relative composition of starting materials and products using the equation. The atmospheric mass spectrometry measured the hydrogen produced in the hydrogenation compartment and an electrochemical compartment in the membrane reactor.
The palladium membrane permeated 73%hydrogen with an average ionic current of 27 picoamperes in the hydrogenation compartment and 10 in the electrochemical compartment. In contrast, another membrane showed less than 1%permeation to hydrogen. GC-MS of hydrogenation under an electrochemical bias showed a sharp peak of the starting material propiophenone as the reaction progressed forming peaks represented propylbenzene and 1-Phenyl-1-propanol, while the propiophenone peak diminished.
In contrast, propiophenone was not converted to the product when the palladium membrane was not electrochemically biased. However, the chromatogram displayed an unexpected peak attributed to an impurity. Under an electrochemically biased palladium membrane, the kinetic profile of the hydrogenation reaction demonstrated the composition change in starting material and products.
In contrast, when the palladium membrane was not electrochemically biased, starting material composition was not changed as the product was not formed. It's important to assemble the reactor to prevent leakage between compartments. Sample the reaction with a precise instrument like a micro pipette to ensure quality data from the GC-MS.
Additional characterization methods like H NMR can be performed to confirm the chemical structure of the reaction products.
