**3. Materials and Methods**

### *3.1. Fabrication and Characterization of the Catalysts*

Ga partially substituted hydrotalcite defined by a M2+/M3+ ratio of 2 (where M2+ = Mg2+ and M3+ = Al3+ and Ga3+), are obtained by a standard co-precipitation method at a constant pH [13,15] and denoted as MgGaAl. More precisely, the aqueous solutions of Mg(NO3)2·6H2O, Al(NO3)3·9H2O and GaSO4·7H2O were added to a solution of Na2CO3/NaOH at a constant pH of 9.5 and the precipitate was aged for 24 h at 45 ◦C. Further, after the calcination at 550 ◦C for 8 h, the evolved mixed oxides were denoted as MgGaAlcal. Heterostructures of the LDH with plasmonic Au and Ag was achieved in aqueous medium during the structural reconstruction of the LDHs, in the aqueous solutions of Au(CH3COO)3 and Ag2SO4, respectively, at room temperature [33,40] and Au and Ag mass content were calculated to reach ~4.0% mass loading. The heterostructured catalysts were denoted as Au\_MgGaAl and Ag\_MgGaAl, respectively. After calcination at 550 ◦C for 8 h the derived catalysts were denoted as Au\_MgGaAlcal and Ag\_MgGaAlcal.

X-ray diffractions were performed on a PANalytical X'Pert ((Malvern PANalytical Ltd., Almelo, The Netherlands) PROMPD diffractometer equipped with a filtered Cu Kα radiation; measurements were done in the 2θ mode using a bracket sample holder with a scanning speed of 0.04◦/4 s in continuous mode. Diffuse Reflectance Infrared Fourier Transform spectra (DRIFT) were measured on a Nicolet 6700 FT-IR spectrometer (Thermo, Waltham, MA, USA), equipped with a mid-IR source (400–4000 cm<sup>−</sup>1), a KBr-beam splitter and about 200 scans were taken with a 4 cm−<sup>1</sup> resolution. TEM/HRTEM images and results were obtained on Ultra-High resolution TEM microscope, UHR-TEM-Libra 200 MC/Carl Zeiss GmbH (Carl Zeiss Microscopy GmbH, Oberkochen, Germany). X-ray photoelectron spectroscopy (XPS, PerkinElmer Inc., Waltham, MA, USA) spectra were recorded using a Perkin-Elmer Model 5500-MT spectrometer equipped with Mg Kα radiation (1253.6 eV), operating at 15 kV and 20 mA; the binding energies (BE) were corrected by referencing the C1s peak to 284.8 eV. The UV-vis analysis profiles were acquired with a Jasco 500 UV-vis spectrophotometer within the wavelength range of 200–800 nm.
