The Controlled Catalytic Oxidation of Furfural to Furoic acid using AuPd/Mg(OH)2

Furfural is a platform chemical formed from lignocellulosic biomass and whilst its applications are somewhat limited, further processing can lead to the production of other high value products. This body of work describes the use of a 1% AuPd/Mg(OH)2 catalyst for the selective oxidation of furfural to furoic acid. The current industrial method for the production of furfural from furoic acid utilizes a homogeneous Cannizzaro reaction which is initiated by NaOH. In this study we highlight the potential benefits which can be gained by using a heterogeneous Au containing catalyst for this process and provide a detailed understanding how certain variables such as the reaction conditions and Au:Pd ratio can drastically effect the reaction selectivity and rate.

The corresponding data file contains the data which were used to produce the figures in the corresponding published manuscript. A brief explanation of each figure is provided below.

 Tab 1 [Figure 1]: Transmission electron microscopy (TEM) was used to determine the average particle size of the supported Au/Pd nanoparticles in the fresh AuPd/Mg(OH)2 catalyst. Images captured from the TEM were processed using ImageJ. The corresponding particles sizes measured are displayed in the list in Tab 1. From this, the quantity of particles lying within specified sizes were recorded and displayed in a histogram in Tab 1 along with a TEM image which was used in the particle size measurement.

 Tab 2 [Figure 2(a)]: Data corresponding to reactions which were conducted from furfural (0.24 mL in 10 mL of H2O) in the presence of NaOH (0.3 M) and the 1% AuPd/Mg(OH)2 catalyst (at a ratio of 500 moles of furfural to 1 moles of Au+Pd). Each reaction was conducted six times and the mean of the furfural concentration (M), furfuryl alcohol concentration (M), furoic acid concentration (M) and the mean of the carbon mass balance [CMB] (%) was calculated at different reaction times (0.5, 1, 2 and 4 h; displayed in the time online plot in Tab 2, with error bars determined from the standard deviation. Reaction conditions: 303 K, pressure: 3 bar O2, NaOH: FF molar equivalents: 1. *M is molar concentration, h is time in hours, mL is millilitres and K is temperature in K.

 Tab 3 [Figure 2(b)]: Data corresponding to reactions which were conducted from furfural (0.24 mL in 10 mL of H2O) in the presence of NaOH (0.3 M) and in the absence of the 1% AuPd/Mg(OH)2 catalyst. Each reaction was conducted three times and the mean of the furfural concentration (M), furfuryl alcohol concentration (M), furoic acid concentration (M) and the mean of the carbon mass balance [CMB] (%) was calculated at different reaction times (0.5, 1, 2 and 4 h); displayed in the time online plot in Tab 3, with error bars calculated from the standard deviation. Reaction conditions: 303 K, pressure: 3 bar O2, NaOH: FF molar equivalents: 1. *M is molar concentration, h is time in hours, mL is millilitres and K is temperature in K.

 Tab 4 [Figure 2(c)]: Data corresponding to reactions which were conducted from furfuryl alcohol (0.255 mL in 10 mL of H2O) in the presence of NaOH (0.3 M) and in the 1% AuPd/Mg(OH)2 catalyst (0.091 grams). Each reaction was conducted three times and the mean of the furfural concentration (M), furfuryl alcohol concentration (M), furoic acid concentration (M) and the mean of the carbon mass balance [CMB] (%) was calculated at different reaction times (0.5, 1, 2 and 4 h); displayed in the time online plot in Tab 4, with error bars calculated from the standard deviation. Reaction conditions: 303 K, pressure: 3 bar O2, NaOH: FF molar equivalents: 1.  *M is molar concentration, h is time in hours, mL is millilitres and K is temperature in K.

 Tab 5 [Figure 3]: A schematic diagram corresponding to the proposed reaction mechanism which takes place from the oxidation of furfural in the presence of the 1 % AuPd//Mg(OH)2 catalyst.

 Tab 6 [Figure 4]: Thermogravimetric analysis (TGA) of (a) the fresh 1% AuPd/Mg(OH)2 catalyst, (b) the used AuPd/Mg(OH)2 tested at a reaction temperature of 303 K and (c) the used AuPd/Mg(OH)2 tested at a reaction temperature of 343 K. In each case, the catalyst samples were heated at a ramp rate of 5 K min−1 in air from 303 K to 1000 K. The mass loss from the catalyst is reported as a percentage of the total mass lost. A graph depicting the losses of mass as a function of temperature (K) is also displayed in Tab 6. *K is temperature in Kelvin and min is time in minutes.

 Tab 7 [Figure 5]: Reaction data corresponding to a reusability study, the aim of which was to determine whether there was a drop in catalytic performance as it was used in subsequent reactions. Each catalyst ID corresponds to the following: Fresh (fresh 1% AuPd/Mg(OH)2 catalyst), Re-use 1 (1% AuPd/Mg(OH)2 catalyst which has been used once before), Re-use 2 (1% AuPd/Mg(OH)2 catalyst which has been used twice before) and so on. For each catalyst the yield of furoic acid and the carbon mass balance (CMB) is displayed at different reaction times (0.5 and 4 h). The calculated turnover frequency (TOF) which corresponds to the yield of furoic acid produced at 0.5 h is also displayed. A graph is highlighting how the yield of furoic acid, the CMB and the TOF is effected by subsequent catalyst uses. In each case reactions were conducted from furfural (0.24 mL in 10 mL of H2O) in the presence of NaOH (0.3 M) and catalyst (0.091 grams). Reaction conditions: 303 K, pressure: 3 bar O2, NaOH: FF molar equivalents: 1. *M is molar concentration, h is time in hours, mL is millilitres and K is temperature in K.

 Tab 8 [Figure 6]: Transmission electron microscopy (TEM) was used to determine the average particle size of the supported Au/Pd nanoparticles in each of the used  AuPd/Mg(OH)2 catalysts. Each catalyst ID corresponds to the following: Re-use 1 (1% AuPd/Mg(OH)2 catalyst which has been used once before), Re-use 2 (1% AuPd/Mg(OH)2 catalyst which has been used twice before) and so on. Images captured from the TEM were processed using ImageJ. For each catalyst, the corresponding particles sizes measured are displayed in a labelled list in Tab 8. From this, the quantity of particles lying within specified sizes were recorded and displayed in a histogram. Each histogram is also displayed in Tab 8 along with a TEM image used in the particle size measurement.

 Tab 9 [Figure 7]: Reaction data highlighting the relationship between Au and Pd content in the catalyst. The furoic acid yield is displayed 0.5 and 4 h and the carbon mass balance is displayed after 4 h of reaction. Each figure corresponding to a yield of furoic acid is normalised in accordance to a total metal loading of 1 wt.%. In each case reactions were conducted from furfural (0.24 mL in 10 mL of H2O) in the presence of NaOH (0.3 M) and catalyst (0.091 grams). Reaction conditions: 303 K, pressure: 3 bar O2, NaOH: FF molar equivalents: 1. *M is molar concentration, h is time in hours, mL is millilitres and K is temperature in K.

 Tab 10 [Figure 8]: Initial rates of reaction are displayed for the oxidation of furfural in the presence of a 1% AuPd/Mg(OH)2 catalyst and in the absence of any catalyst (Cannizzaro reaction). For both circumstances, the temperature is varied as stated in the document. In each case reactions were conducted from furfural (0.24 mL in 10 mL of H2O) in the presence of NaOH (0.3 M) and catalyst (0.091 grams) when used. Reaction conditions: Pressure: 3 bar O2, NaOH: FF molar equivalents: 1. The natural logs of the rate constants are subsequently calculated and plotted against 1/K in order to derive Arrhenius plots for both reactions. *M is molar concentration, h is time in hours, mL is millilitres and K is temperature in K.

 Tab 10 [Figure S1]: Powder X-ray diffraction (XRD) data corresponding to (a) the MgO support and (b) the fresh AuPd/Mg(OH)2 catalyst. *θ is the diffraction angle.

 Tab 11 [Figure S2]: Powder X-ray diffraction (XRD) data corresponding to (a) the fresh AuPd/Mg(OH)2 catalyst and (b) the AuPd/Mg(OH)2 catalyst after calcination (heating in air) at 673 K for 2 h. *K is temperature in Kelvin, h is time in h and θ is the diffraction angle.

 Tab 12 [Figure S3]: Powder X-ray diffraction (XRD) data corresponding to (a) the fresh AuPd/Mg(OH)2 (b) after one use, (c) after two uses, (d) after three uses and (e) after four uses. *θ is the diffraction angle.

 Tab 13: Calibration graphs for furfural, furoic acid and furfuryl alcohol. Solutions of differing concentrations of each compound were made and assessed by high performance liquid chromatography (HPLC). Products were separated using a Metacarb 67H column using an aqueous H3PO4 (0.01 M in H2O) mobile phase at a flow rate of 0.25 mL min−1. A diode array detector (DAD) was used and each component was assessed at a wavelength of 210 nm. For each compound, the areas determined for each integrated peak is plotted against the concentration of each solution (M). The subsequent gradient of the trend line was used as the corresponding response factor. *M is molar concentration, min is time in minutes, mL is milliliters and nm is wavelength in nanometres.

Research results based upon these data are published at  http://doi.org/10.1039/c7cy01025g