*2.2. Catalyst Preparation and Characterization*

The catalysts were prepared via an incipient wetness co-impregnation method. The detailed characterization of the catalyst has been previously described [27]. The Al-MCM-41 supported catalysts had a mesoporosity structure, with a pore size of around 3 nm. The total acidity of the Al-MCM-41 support measured by temperature programmed desorption (TPD) of ammonia was 1.06 mmol/g. The transmission electron microscopy (TEM), temperature programmed reduction (TPR) in hydrogen, and powder X-ray diffraction (XRD) results implied that the addition of Pd could improve the dispersion and reducibility of Co and Fe oxides with the formation of Pd–Co and Pd–Fe alloys.

Thermogravimetric analysis (TGA) under the flow of air was conducted in a TA Instrument model QA50. During the TGA analysis, temperature was increased from room temperature to 900 ◦C, at a heating rate of 10 ◦C/min. X-ray photoelectron spectroscopy (XPS) was performed with a Thermo Scientific K-Alpha system equipped with an Al Kα radiation source. The spectrometer was operated with the constant analyzer energy (CAE) mode at a pass energy of 50 eV and a step of 0.1 eV. Quantification and deconvolution were performed using the Gaussian functions of the OriginPro 2015 software (OriginLab, Northampton, MA, US).

### *2.3. HDO of Guaiacol*

A Catalytic HDO reaction was conducted in a fixed-bed reactor at 400 ◦C and ambient pressure. The details of the experimental set-up of the HDO of guaiacol were mentioned in a previous report [27]. Before the HDO reaction, all the catalysts were reduced to 450 ◦C using a hydrogen flow of 90 mL/min for 2 h. Pure guaiacol was fed at a flow rate of 1.08 mL/h using a syringe pump and vaporized at 350 ◦C in the top glass wool bed. Catalyst regeneration was carried out after 210 min of guaiacol HDO reaction. The used

catalyst was first treated with an air flow at 500 ◦C for 240 min. Afterwards, the catalyst was reactivated in hydrogen flow at 450 ◦C for 120 min and catalyzed a new HDO reaction cycle. The liquid products were quantified by a Shimadzu GC-2014 gas chromatography (GC), with a SGE BPX–5 capillary column (30 m, ID 0.25 mm, and 0.25 µm) and a flame ionized detector (FID). The gas products were analyzed by a Shimadzu GC–8A system equipped with a thermal conductivity detector (TCD). The carbon balance of the HDO experiments was between 93% and 98%. The HDO of guaiacol over the Pd–Fe catalyst at W/F of 1.67 h and temperature of 400 ◦C were repeated twice, and the standard deviation of all product yields was less than 1.0 MolC%. Meanwhile, the other HDO experiments were conducted once. Carbon-based guaiacol conversion (*XGua*), product yields (*Y<sup>i</sup>* ), and HDO yields were calculated in MolCarbon% by the following equations.

$$X\_{Gua} \left( \% \right) = \frac{Mol(gua)\_{in} - Mol(gua)\_{out}}{Mol(gua)\_{in}} \times 100 \tag{1}$$

$$Y\_i \text{ (\%)} = \frac{Mol\_i \times a\_i}{Mol (gua)\_{in} \times a\_{gas}} \times 100\tag{2}$$

$$HDO \, yield\left(\%\right) = \sum\_{i=1}^{25} \frac{Y\_i \times \left(\beta\_{gas} - \beta\_i\right)}{\beta\_{gas}}\tag{3}$$

where α*<sup>i</sup>* and *β<sup>i</sup>* are the carbon and oxygen numbers in the product *i*; *αgua* = 7 and *βgua* = 2.

### **3. Results**
