*2.5. Catalytic Tests*

A lab scale autoclave reactor (100 mL capacity from Parr) (Parr Instrument Company, Moline, IL 61265-1770, USA), equipped with a mechanical stirrer (0–600 rpm) and sensors for temperature and pressure measurement, was used to carry out the catalytic tests. An aqueous solution of HMF (25 mL, 18 mM) and NaOH (NaOH/HMF molar ratio = 2) and the membrane previously cut into small squared pieces of 1 cm<sup>2</sup> (HMF/total metal molar ratio = 100) were loaded in the reactor. To perform the reactivity tests, the autoclave reactor was purged three times with O<sup>2</sup> (2 bar) and then pressurized at 10 bar. The temperature was increased to the set point and the reaction mixture was stirred at 600 rpm for the whole duration of the experiment (4 h if not stated differently). As reaction initial time (time zero) for the reaction was considered when the set point temperature was reached (after 10 min). At the end of the reaction, the reactor was cooled down to RT and the solution was filtered. Then, the reaction mixture was diluted five times and then analyzed with an Agilent Infinity 1260 liquid chromatograph equipped with an Aminex HPX-87H 300 mm × 7.8 mm column (0.005 M H2SO<sup>4</sup> solution as mobile phase) and a DAD. Compound quantifications were performed from the peak areas after calibration using commercially available samples. Recycling tests have been performed by reusing the recovered membrane without any further cleaning procedure.

#### **3. Results and Discussion** *Processes* **2020**, *8*, 45 5 of 15

The preparation of monometallic Au and bimetallic Au/Pd (molar ration 6/1) was optimized elsewhere [24] and led to the formation of small nanoparticles, having mean nanoparticle diameter of 4 and 4.5 nm for Au and AuPd NPs, respectively (revealed by XRD analysis and TEM—Table S4). Their impregnation on TiO2, with a metal lading of 1.5%, leads to slight mean particle size increase (Figures S3 and S4). The preparation of monometallic Au and bimetallic Au/Pd (molar ration 6/1) was optimized elsewhere [24] and led to the formation of small nanoparticles, having mean nanoparticle diameter of 4 and 4.5 nm for Au and AuPd NPs, respectively (revealed by XRD analysis and TEM—Table S4). Their impregnation on TiO2, with a metal lading of 1.5%, leads to slight mean particle size increase (Figures S3 and S4).

### *3.1. PAN-Based Catalytic Membranes 3.1. PAN-Based Catalytic Membranes*

observed by SEM (Figure 1) and TEM (Figure 2).
