*3.3. Experimental Methodology*

#### 3.3.1. Preparation of Ni-UGSO

Ni-UGSO is prepared via a solid-state reaction developed by Chamoumi et al. [16]. In summary, UGSO was first milled and sieved in a 53 μm sieve, which was the smallest size obtained with our dry powder sieving equipment. Nitrate hexahydrate Ni(NO3)2·6H2O was used as a Ni precursor; the latter was mixed with the UGSO in the targeted proportion. A small quantity of water was added, and the mixture was then milled and homogenized softly in a mortar at ambient temperature. The resulting milled mixture was oven-dried at 105 ◦C for 4 h and then calcined at 900 ◦C for 12 h. After calcination, the catalyst was sieved down to 53 μm and was used in the catalytic tests as powder dispersed in the quartz wool placed in the differential reactor.

#### 3.3.2. Activation of Ni-UGSO

The Ni-UGSO was activated by H2. The evolution of the catalyst structure was studied using TPR, TEM and XRD analysis. The catalyst was activated under a flow of 75% H2 and 25% Ar for a time-on-stream (TOS) of 2 h. Table 11 shows the activation test conditions.


**Table 11.** Activation test conditions.

Gases are fed at atmospheric pressure.

#### 3.3.3. Dry Reforming (DR) and Catalytic Cracking (CC) Reactions

Ni-UGSO was used as a catalyst for ethylene DR and CC. The influence of two factors was studied:


In order to choose the temperature range for the tests, a study of thermodynamic equilibrium was done at temperatures ranging from 350 ◦C to 850 ◦C (Section 2.3.1). The wt.% of Ni in the catalyst, 13%, was chosen because the theoretical calculations based on the average UGSO composition show that this Ni content is necessary if all available Fe and Al oxides form spinels with Ni [30]. Nevertheless, since the catalytic activity comes from the local reduction of Ni and Fe into their metallic forms, as well as the concentration of these species at the surface of their support, lower Ni percentage were tested as well. Therefore, 10% and 5% were chosen arbitrarily as intermediate and lower wt.% of Ni.

A 32 fully reproduced factorial design of experiments (18 runs) were conducted for each study (nine tests with their duplicates). The experiments were conducted at atmospheric pressure after the activation step. Reaction conditions are summarized in the Tables 12 and 13.


**Table 12.** Ethylene dry reforming (DR) reaction conditions.


**Table 13.** Ethylene catalytic cracking (CC) reaction conditions.


a Gases are fed at atmospheric pressure.
