*3.2. Catalyst Preparation*

The required amounts of Ni(NO3)2.6H2O, Ce (NO3)3.6H2O, Mg (O2CCH3)2.4H2O, and support were mixed and were ground together to fine powder by pestle and mortar. A small amount of ultrapure water was used to convert the solid mixture into a paste, which was spun mechanically until dryness. The paste and spinning process was repeated three times. The final solid was calcined in a digital, programmed muffle furnace at 600 ◦C for three hours by ramping temperature from room temperature by a rate of 3.0 ◦C/min. The notation of the prepared catalyst samples and their wt. % loadings of nickel oxide, ceria, and magnesia at 600 ◦C calcination are given below in Table 4.


**Table 4.** Prepared catalyst samples and the wt. % of their composition.

## *3.3. Catalyst Characterization*

The metallic component composition of all catalysts was determined by an Agilent 7800 inductively coupled plasma mass spectrometry (ICP) at the laboratory of IDAC Merieux NutriSciences, Riyadh, Saudi Arabia. Carbon deposition on the used catalysts was measured by thermogravimetric analysis (TGA) under air by using a Shimadzu TGA-51(Shimadzu Corp., Kyoto, Japan). A certain amount from the spent catalyst (10 mg) was subjected to heat treatment within the temperature range 25 ◦C–1000 ◦C. Ramping temperature was maintained at 20 ◦C/min. Temperature programmed oxidation (TPO) was performed in an oxidative atmosphere to determine the kind of carbon deposited over the surface of the catalyst using Micromeritics AutoChem II over a temperature range of 50–800 ◦C under a flow of 10% O2/He mixture at 40 mL/min. The spent catalyst was first pretreated in the presence of high purity Argon at 150 °C for 30 min and subsequently cooled to room temperature. The Brunauer-Emmet-Teller technique was adopted in calculating the surface area per unit mass of the samples using a device that analyses surface area and porosity, i.e., Micromeritics Tristar II 3020 (Micromeritics Instrument Corporation, Norcross, GA, USA). For nitrogen physisorption measurements, an amount of 0.20–0.30 g weighed from the catalyst was subjected to degassing at 300 ◦C for three hours prior to analysis. The reducibility of the fresh catalysts was determined by the Micromeritics AutoChem II (Micromeritics Instrument Corporation, Norcross, GA, USA). A sample weight of 75.0 mg was analyzed. Samples were first heated under argon (99.9%) at 150 ◦C for 30 min, thereafter cooled to 25 ◦C. Afterwards, samples were heated to 1000 ◦C at 10 ◦C/min by allowing the flow of 10% H2/Ar gas at 40 mL/min. A thermal conductivity detector (TCD) was used to follow the H2 consumption. Temperature programmed desorption of carbon dioxide (CO2-TPD) and CO pulse chemisorption measurements were obtained from an automatic chemisorption equipment (Micromeritics AutoChem II 2920) with a TCD. At the start, a 70 mg sample was heated at 200 ◦C for 1 h under helium (He) flow to remove adsorbed components. Then, CO2 adsorption was carried out at 50 ◦C for 60 min in the flow of He/CO2 gas mixture (90/10 L/L) with a flow rate of 30.0 mL/min. Afterwards, a linear temperature rise at a rate of 10 ◦C/min until 800 ◦C was registered by the TCD of CO2 desorption signal. The nickel metallic surface area and dispersion were determined by H2 pulse chemisorption by using Micromeritics AutoChem II. A sample of 50.0 mg was heated to 150 ◦C under vacuum for sixteen hours. The sample was then transferred to the sample tube and was heated at temperature rate of 10.0 ◦C/min to 400 ◦C under flow rate of 10.0 mL/min of 10%H2/Ar for one hour. The sample was then flushed with highly pure Ar for one hour at 400 ◦C. The temperature was then reduced to 70.0 ◦C and pulses of H2 gas were introduced for one hour for determining the H2 uptake. X-ray powder diffraction patterns for the samples were recorded on a Bruker D8 Advance (Bruker, Billerica, MA, USA) XRD diffractometer by using Cu Kα radiation source and a nickel filter, operated at 40 kV and 40 mA. The step size and scanning range of 2θ for analysis was set to 0.01◦ and 5–100◦, respectively. The present phases were documented using standard powder XRD cards (JCPDS). Catalyst morphology was studied using JEOL JSM-7100F (JEOL, Tokyo, Japan) (field emission scanning electron microscope, equipped with energy-dispersive X-ray spectroscopy (EDXS) for surface elemental analysis.
