**2. Synthesis, characterization, and catalytic activity of noble (Ru, Au, Ag) and based (Cu) metal nanoparticles supported applied in the CWAO of fuel oxygenated**

## **2.1 Synthesis of Al2O3 and Al2O3-CeO2 by wet impregnation and precursor calcination**

 The synthesis methods occupied for the production of supported catalysts include different techniques or procedures based on a phenomenon of precipitation, chemical adsorption, hydrolysis-polymerization, etc. These methods can synthesize supported catalysts in a single step, or in two steps, that is, both the precursor salt of the support and the active phase are added in the reaction mixture in a single step; otherwise, in sequential or two steps, first the support is synthesized, usually an oxide, and then the active phase, usually a metal, is prepared by some other specific method, expecting all the metal to be added and adsorbed on the support, without metal loss and with a high metal dispersion [20, 21].

 These methods determine important properties such as homogeneous metal dispersion, high specific surface area, adequate acidity/basicity ratio, metal-support interaction, and generation of structural defects, for example, oxygen vacancies and reducibility; an improvement in the catalytic performance is concluded owing to the development of these properties in the synthesized catalysts [22, 23]. So in this, study we evaluated different synthesis methods for the catalysts tested in CWAO from oxygenated fuels.

The γ-alumina was obtained by the calcination of boehmite Catapal-B (AIO(OH)), in this process an amount of boehmite (AIO(OH)) is deposited in a

#### *Nonconventional Wastewater Treatment for the Degradation of Fuel Oxygenated… DOI: http://dx.doi.org/10.5772/intechopen.84250*

fixed-bed quartz reactor in which a continuous flow of air of 1 cm3 /s is passed, and then the calcination is carried out, at a temperature of 650°C for 4 h.

Wet impregnation method was used to prepare the Al2O3-CeO2 support. Ceria is incorporated into the boehmite (AIO(OH)) with an aqueous solution of Ce(NO3)3.6H2O (necessary amount of salt to obtain 1, 3, 5, 7.5, and 10% weight) in 100 ml of distilled water. The precursor solution of ceria is previously deposited in a ball flask, the boehmite is added to this solution and left to stir for 3 h in a rotary evaporator, and then the solution is dried with constant agitation at 60°C to evaporate the water excess. After impregnation, the obtained solid sample was dried at 120°C for about 16 h and calcined at a temperature of 650°C in air flow of 1 cm3 /s for 4 h. The CeO2 support was obtained commercially.

#### **2.2 Synthesis of noble and base metal catalysts by wet impregnation**

The solid catalysts reported in the literature that are used in the oxidation of water pollutants can be classified into four groups: supported metal oxides, unsupported metal oxides, supported metals, and mixtures of noble metals and metal oxides. The type of supported metal is composed mainly of noble and base metals. These are also very important to influence catalyst activity. Noble metals such as Ag, Au, Ru, Pd, Rh, and Pt are very active elements for oxidation reactions; they reveal high activities and excellence stability; however, their high cost and limited availability can decrease their applicability. Base catalysts such as Ni and Cu are more interesting systems, and a lot of research is being done to improve their stability because by having a lower cost, compared to noble metals, they are an economical option; they are also active, but less stable, and suffer from carbon deposit and metal leaching [24, 25].

 Cu catalysts supported on Al2O3 were synthesized by wet impregnation in a single step. A calculated amount of copper nitrate to obtain a concentration by weight of 5, 10 and 15wt% in copper plus an adequate amount of boehmite Catapal-B were dissolved in 100 ml of water; then the solution was adjusted to a pH of 1, with the addition of a drop of HNO3, and stirred for 4 h, regulating the temperature from 70 to 90°C. After impregnation, the obtained solid sample was dried at 120°C for about 12 h and calcined at a temperature of 400°C in airflow of 1 cm3 /s for 4 h. Cu (5wt%)/Al2O3, Cu (10wt%)/Al2O3, and Cu (15wt%)/Al2O3 are the monometallic Cu catalysts supported in alumina, synthesized by wet impregnation method in a single step, which later we will name as Cu5AlIH, Cu10AlIH, and Cu15AlIH.

Copper catalysts supported on Al2O3 were also synthesized by sol-gel in a single step. An aqueous solution of 10 ml of aluminum trisecbutoxide ([C2H5CH(CH3) O]3Al), 97% aldrich, d = 0.96 g/mol with 4 g of urea and copper nitrate adequate amount in grams for the percentages of 5, 10, and 15wt% in 1-butanol was progressively added, between 70 and 90°C to a mixture of water and butanol, under constant stirring. After 24 h reflux at 70°C, the resulting pseudo-gel was dried in in a rotating evaporator at 120°C for 12 h and then calcined at 400°C for 4 h. It is worth mentioning that a catalyst was prepared with a pyrrolidine additive instead of urea, exclusively with the same quantities of reagents as the 15wt% in Cu. The synthesized monometallic catalysts will be named as Cu5AlSG, Cu10AlSG, Cu15AlSG, and Cu15AlSGp.

Finally, the monometallic Cu/Al2O3 catalysts were synthesized by wet impregnation with urea and with a concentration by weight of 5, 10, and 15wt% of the metal. A calculated amount of boehmite Catapal-B was dissolved in 300 ml of deionized water; then the solution was adjusted to a pH of 3 with the addition of 1 ml of HNO3 and stirred for 2 h. After that, 200 ml of a solution of cupric nitrate [Cu(NO3)2 ½H2O] and urea is added dropwise to the solution of boehmite Catapal-B, regulating the temperature from 70 to 90°C. After impregnation, the obtained solid

 sample was washed three times with hot water and dried at 120°C, and finally it was calcined at a temperature of 400°C for 4 h. It should be noted that a catalyst was prepared with a pyrrolidine additive instead of urea, exclusively with the same amounts of reagents as the 15wt% in Cu. The synthesized monometallic catalysts will be named as Cu5AlIHU, Cu10AlIHU, Cu15AlIHU, and Cu15AlIHp.

 Ru-supported catalysts were prepared by wet impregnation method of Al2O3 and Al2O3-CeO2 supports aggregating the appropriated amounts of an aqueous solution containing RuCl3\* XH2O to obtain a nominal concentration of 2wt% of Ru, adding 100 ml of hydrochloric acid 0.1 M. First Al2O3 and Al2O3-CeO2 (1.0, 3.0, 5.0, 7.5, and 10wt% of Ce) support was wetted by distilled water in a beaker in order to have high dispersion and to maximize the mass transfer of added metal salt (RuCl3\* XH2O) on the surface and the pores of the catalyst. The resulting solution is stirred for 1 h; after that it is heated at 60°C. The samples were dried at 120°C for 24 h and then calcined under air flow (60 ml/min) at 650°C for 4 h, with a heat rate of 2°C/ min. Finally, the catalysts were reduced under H2 (60 ml/min) at 400°C for 5 h, with a heat rate of 2°C/min. The synthesized monometallic catalysts will be named as RuAlIH, RuAlCe1IH, RuAlCe3IH, RuAlCe5IH, RuAlCe7.5IH, and RuAlCe10IH.

#### **2.3 Synthesis of noble and base metal catalysts by deposition-precipitation**

 Deposition of gold into the modified supports was carried out by the method of deposition-precipitation using urea according to the procedure described below. Support powder (Al2O3, CeO2, Al2O3-CeO2 (1wt%), Al2O3-CeO2 (5wt%), Al2O3-CeO2 (10wt%) was first dispersed in distilled water. The temperature of the suspension was kept constant at 80°C and agitated with a magnetic stirrer. Secondly, the requisite quantity of chloroauric acid (HAuCl4) solution was added to the suspension, and the temperature was let to stabilize. Thirdly, 2.33 g of urea was added into the reactor vessel, and the suspension was stirred continuously for 16 h. The deposition was followed by centrifugation of the catalyst suspension in 50 ml tubes. The centrifugation was conducted three times. Separated water was decanted away, and the tube was refilled with distilled water after the first and the second centrifugations. Posterior the following separation and washing, the solid was collected and moved to a rotary evaporator and dried at 60°C in a water bath under vacuum. Final drying was done in an oven at 120°C overnight. All catalysts were calcined in air flow by heating them from room temperature up to 300°C for 4 h. The synthesized monometallic catalysts will be named as AuAlDPU, AuCeDPU, AuAlCe1DPU, AuAlCe5DPU, and AuAlCe10DPU.

The supported Ag nanoparticles were synthesized by DP with NaOH. The procedure was the same as the described for the gold synthesis by DP with urea, only that, instead of urea, NaOH was occupied, regulating solution's pH to 9. The synthesized monometallic catalysts will be named as AgCeDPNa, AgAlDPNa, AgAlCe1DPNa, AgAlCe3DPNa, AgAlCe5DPNa, AgAlCe7.5DPNa, and AgAlCe10DPNa. All the catalysts prepared are mentioned in **Table 1**.

### **2.4 Characterization of noble (Ru, Au, Ag) and base (Cu) metal nanoparticles supported**

 **Figure 1** shows the adsorption isotherms of the synthesized materials of RuAlIH and RuAlCe1IH. It was observed that both isotherms are of type IV, which were associated with capillary condensation in mesoporous catalysts, where the hysteresis loops indicated that the pores are well distributed.

For the catalysts of RuAlIH and RuAlCe1IH (the other TPR analyzes the rest of the catalysts not shown), **Figure 2** which displayed a main peak of 36–52°C was


#### *Nonconventional Wastewater Treatment for the Degradation of Fuel Oxygenated… DOI: http://dx.doi.org/10.5772/intechopen.84250*


**Table 1.** 

*Lists the Cu, Ag, Au, and Ru catalysts supported on Al O2 3, CeO2, and Al O2 3-CeO2, tested in CWAO of fuel oxygenated (FO) with the operating conditions: T = 100°C, P(O2) = 10 bar, VLiq = 0.25 l, CFO = 1000 mg/l, CCat = 1 g/l, and ω = 1000 rpm.*  *Nonconventional Wastewater Treatment for the Degradation of Fuel Oxygenated… DOI: http://dx.doi.org/10.5772/intechopen.84250* 

**Figure 1.**  *Adsorption isotherms of (a) RuAlIH and (b) RuAlCe1IH.* 

**Figure 2.**  *H2-TPR profiles of the catalysts RuAlIH and RuAlCe1IH.* 

 observed which indicates that the reduction is carried out in that first peak, and it was attributed to the oxidation change of Ru from +2 to 0 (RuO) since it was the species that was reduced first. The second signal observed at 135–142°C was attributed to ruthenium oxide (RuO2), with an oxidation state of +4 which passes from +4 to +2 and subsequently to 0. On the other hand, the two peaks clearly observed in **Figure 2** 

indicated that the ions of Ru existed in two different states to be reduced with hydrogen, meaning that at the end of the reduction, only the states +2 and 0 remain.

 **Figure 3** corresponds to the diffraction patterns of the catalysts containing Au. It showed only signals corresponding to Al2O3 and CeO2, and only a decrease of the alumina signal was observed when the content of Al2O3-CeO2 increases by 10%. The corresponding Au signals were not shown in this diffractogram due to the weight % in which the catalysts were prepared, and in XRD only the metal was observed at concentrations higher than 2 and sometimes 3%.

 In **Figure 4**, the H2-TPR profiles of the Au-supported catalysts revealed that the first reduction peaks (around 50°C) appearing for all Au-supported catalysts corresponded to the highly dispersed Au peaks on the catalyst surface. This signal increased to values higher than 50°C in the case of the Au catalyst deposited in Ce which indicates a difference in the size of the particles (observed by TEM). The second peak (around 100°C) was attributed to a second oxidation state of Au that interacts with Ce. This signal increased with the Ce content. This can be supported since in the AuAlDPU catalyst, this signal did not appear; however, it appeared in the AuCeDPU catalyst.

 **Figure 5** shows the XRD for the copper catalysts prepared by wet impregnation method, in which γ-Al2O3 phase was seen as well as the intense signals that indicated the presence of CuO, and the boehmite, indicating that the metal was correctly dispersed in the three synthesized catalysts.

#### **2.5. Catalytic evaluation (MTBE, ETBE, TAME)**

#### *2.5.1 Reaction conditions*

The activity level tests of the catalysts synthesized in this study were carried out in a Parr batch 300 ml batch reactor, under the conditions of 100°C, 10 bar, and 1000 ppm of fuel oxygenated. In the standard procedure for a CWAO experiment,

**Figure 3.**  *X-ray diffraction patterns of Au-supported catalysts.* 

*Nonconventional Wastewater Treatment for the Degradation of Fuel Oxygenated… DOI: http://dx.doi.org/10.5772/intechopen.84250* 

**Figure 4.**  *H2-TPR of Au-supported catalysts.* 

**Figure 5.**  *X-ray diffraction patterns for the Cu-supported catalysts synthesized by wet impregnation in a single step.* 

250 ml of fuel oxygenated solution were poured, and 0.25 g of catalyst were placed in the 300 ml reactor. When the selected temperature was reached, stirring was started at a maximum speed of 1000 rpm. This time was taken as the zero reaction time and the reaction duration was 60 min. These conditions were the same for all synthesized materials. The liquid samples were periodically removed from the reactor, then filtered to remove any catalyst particles, and finally analyzed by gas chromatography and total organic carbon (TOC).

With the following equation, the conversion values for total organic carbon and FO were determined at different times with intervals of 30 min up to 180 min of reaction:

$$\mathbf{X\_{TOC}} = \frac{\mathbf{TOC}^0 - \mathbf{TOC}^{60}}{\mathbf{TOC}^0} \times \mathbf{100} \tag{1}$$

$$\mathbf{X}\_{\text{FO}} = \frac{\mathbf{C}\_{\text{o}} - \mathbf{C}\_{\text{60}}}{\mathbf{C}\_{\text{o}}} \times \mathbf{100\%} \tag{2}$$

where *TOC<sup>0</sup>* is *TOC* at t = 0 (ppm), *C0* is *FO* concentration at t = 0 (ppm), *C60*  is *FO* concentration at t = 1 h of reaction (ppm), and *TOC<sup>60</sup>* is *TOC* at t = 1 h of reaction (ppm).

 The initial rate (*ri*) was calculated from *FO* conversion depending on time, using the following equation:

$$\mathbf{r}\_{i} = \left(\frac{\Delta\_{FO}(\%)}{\Delta t \, m\_{cat}}\right) \left(\left[\text{constant}\,\text{matrix}\right]\_{i}\right) \tag{3}$$

 \_\_\_\_\_\_\_ where <sup>∆</sup>*FO*(%) is the initial slope of the conversion curve, [contaminant]i = initial ∆*<sup>t</sup> FO* concentration, and *mcat* = catalyst mass (gcat/l).

So the selectivity was calculated according to the following equation:

$$\mathbf{S\_{CO\_2}} = \frac{\mathbf{X\_{TOC}}}{\mathbf{X\_{FO}}} \times \mathbf{100} \tag{4}$$
