Investigation of the stability of partial hydrophilic (Pd/γ-Al2O3) in the aqueous phase
Nitrate (NO3–) is introduced in drinking water sources from agricultural, household and industrial waste streams. High concentration of nitrate in drinking water is harmful as it reduces to nitrite (NO2–) in the human body. Presence of nitrite in human body is extremely toxic as it is reported to cause cancer or blue baby syndrome. Therefore the removal of nitrate is necessary from drinking water. The nitrate and nitrite removal from water has been attempted using different techniques, including catalytic hydrogenation. This procedure uses hydrogen as reducing agent to catalytically transform nitrite to nitrogen. Several materials have been used as catalysts supports like alumina, titania and activated carbon. The catalytic active site for nitrite hydrogenation is usually a noble metal, either Pd or Pt. To achieve both high activity and selectivity, good contact between the three phases (solid catalyst, H2gas and dissolved nitrite in water) is essential. Therefore, hydrophobic domains on the catalyst are introduced to enhance the mass transfer of H2 gas on the catalytic sites.
Hydrophobic domains are obtained by modifying the surface of catalyst support with a long chain organic molecule, in our case FOTS (perfluorinated-octyltrichlorosilane). The amount of FOTS used is directly related to the surface area of the catalyst support. In order to have good adhesion between the two domains (hydrophilic/hydrophobic), γ-Al2O3 is used that also results in the homogenous distribution of both domains in the desired particle fraction. In the previous work Cristina et al., used a fixed amount of hydrophobic (50%, α-Al2O3) and hydrophilic (50%, γ-Al2O3) powders, and tested exclusively one composite size fraction (40-100μm). Therefore she did not investigate the stability of the hydrophobic materials.
Based on previous work by Cristina et al., we want to make composites with the different particle size fractions. The question is γ-Al2O3 modified with FOTS is stable enough in the aqueous phase, and how long they can maintain the hydrophobic property. Also we can to know whether the particle size have a relation with hydrophobic stability or not. To achieve the catalyst composite, first we will synthesize the catalyst particles that are hydrophobic γ-Al2O3 and hydrophilic Pd/γ-Al2O3, respectively. Hydrophobic domains will be introduced via physically mixing of hydrophobic γ-Al2O3 and hydrophilic Pd/γ-Al2O3 followed by pelletizing, crushing and sieving to obtain the desired particle size fraction. The catalyst composites initially will be characterized using elemental analysis to give the information related to the distribution of hydrophobic sites in the various catalyst fractions. Also XRF (X-ray fluorescence) will be used to determine the metal loading in the catalyst fraction. After the catalyst stir in the water for some time, then recover the catalyst, after drying, via checking the carbon concentration to determine the stability of the hydrophobic site.