# Catalytic Evaluation of Hafnium Modified SiO\({}_{2}\) for the Dehydration of Alcohols
## 2 Materials and Methods  
### Synthesis of Materials  
Pure silicate was synthesized based on the methodology reported by [PERSON] et al. [19]. A known mass of cetyltrimethylammonium (CTABr, Aldrich, 99%), used as a structuring agent, and distilled water were mixed for 15 min under constant stirring. Subsequently, sodium silicate (Na\({}_{2}\)O\({}_{7}\)Si\({}_{3}\), Aldrich) was added and stirred for 30 min at room temperature. A 2M H\({}_{2}\)SO\({}_{4}\) solution was added slowly dropwise to the resulting mixture until a pH of 9 was obtained and stirring continued for another 4 h under ambient conditions. The resulting precipitate was filtered, washed, and dried at 80 \({}^{\circ}\)C for 48 h, followed by a thermal process at 600 \({}^{\circ}\)C for 6 h under a flow of extra-dry air.  
The introduction of hafnium atoms into the pure silicate was carried out during synthesis, at the stage after pH adjustment, at this stage a solution of hafnium tetrachloride (HfCl\({}_{4}\), Aldrich, 98%) was added slowly dropwise until 3.6 and 5.0% mol of metal on the silicate was obtained. The solution was stirred for a period of 4 h at room temperature. The filtering, drying, and calcination process of the Hf-modified SiO\({}_{2}\) was carried out under the same conditions used for the pure silicate. The resulting materials were labeled as; SiO\({}_{2}\), 3.6 Hf/SiO\({}_{2}\), and 5.0 Hf/SiO\({}_{2}\), respectively. A portion of the 3.6 Hf/SiO\({}_{2}\) catalyst was sulfated with a theoretical content of 12 wt.% sulfate ions by the incipient moisture method and heat treated at 500 \({}^{\circ}\)C for 3 h in extra-dry air flow. This material was labeled as 12 SHf/SiO\({}_{2}\).  
The catalysts were characterized by thermal analysis using TA instruments STD 2690 Simultaneous DCS-TGA with a heating ramp of 5 \({}^{\circ}\)C min\({}^{-1}\), by X-ray diffraction at low angles on a SIEMENS D5000 diffractometer in the range of 1\({}^{\circ}\)\(<\)20 \(<\) 10\({}^{\circ}\) with a scanning speed of 0.01\({}^{\circ}\) min\({}^{-1}\) and diffraction patterns at 10\({}^{\circ}\)\(<\) 20 \(<\) 80\({}^{\circ}\) on a BRUKER AXS X diffractometer model D8 ADVANCE. Textural properties of the catalysts were determined by nitrogen physisorption in a Quantachrome model Autosorb-1 instrument. Fourier transform infrared spectroscopy was performed in the 400-4000 cm\({}^{-1}\) range with 16 scans using an ATR cell in a Perkin Elmer Spectrum 100 spectrophotometer. Morphological characterization of the materials was carried out by scanning electron microscopy using a JEOL model 5800 LV microscope and transmission electron microscopy using a Philips CM 200 microscope and a JEOL-2200 FS microscope with a spherical aberration corrector in STEM mode. The nature and acid strength of the solids were determined by pyridine adsorption using a Bruker Vector 22 FTIR spectrophotometer, and the acid strength of the sites was determined by potentiometric titration with n-butylamine. Finally, acidity of solids was evaluated through ethanol dehydration at 300, 325 and 350 \({}^{\circ}\)C. The methanol dehydration at 350 \({}^{\circ}\)C. Catalytic activity tests were performed using a mass of 100 mg of catalyst in a microplant operating at atmospheric pressure and continuous flow to 40 mL/min coupled to a Shimadzu-FID gas chromatograph equipped with a 30 m \(\times\) 0.32 mm SPB-1 capillary column and 1 \(\upmu\)m SUPELCO film with flame ionization detector (FID).