*2.1. Pd Aerogels Chemical Synthesis*

The synthesis of Pd aerogels was carried out by adding 10 mL of a 2 mg/mL solution of PdCl2 (99%, Sigma-Aldrich ReagentPlus®, anhydrous powder, St. Louis, MO, USA) in deionized water into a solution of 240 mg of sodium carbonate (≥99.5%, J.T. Baker®) and 40 mg of glyoxylic acid monohydrate (98% Sigma-Aldrich) (ratio 6:1) in 40 mL of deionized water at 67.5 ◦C (Figure 1) for two hours in all cases. Two different devices were used as a heating source for this initial step of the reaction: conventional heating in a lab oven (CON) and microwave heating (MW). In the case of microwave heating, the reaction temperature was controlled by a thermocouple introduced in the precursor mixture and connected to a proportional–integral–derivative (PID) temperature controller installed in the microwave oven.

**Figure 1.** Procedure for obtaining aerogels using the sol-gel methodology in this work.

Once the first reactions took place, the reduction reaction and gelation process were also carried out by heating the mixture either by conventional heating (CON) or microwave heating (MW) under different operating conditions (i.e., 45 ◦C or 67 ◦C and 7 h or 24 h), as described in Table 1. After the gelation process, hydrogels were washed several times using deionized water and ethanol to remove the organic residues in the aqueous solution. Before submitting the clean samples to the lyophilization process, they were frozen with Liquid N2, with a volume of 3 mL of deionized water and finally they were dried in a lyophilizer (LYO). A conventional drying in a lab oven (CON) was also performed for comparative proposes.


**Table 1.** Synthesis procedures and operating conditions to obtain the aerogels of this work.
