**4. Conclusions**

This paper investigated the dry reforming of methane, CH4, over Ti-CAT-V catalyst, and the effects of promoters such as CeO2 and MgO, on the catalytic activity and stability of the catalyst. The promoter loading was 10.0 wt. % and 1.0 wt. % for CeO2 and MgO, respectively. Promoted Ti-CAT-V catalyst showed better conversion of both CH4 and CO2 than the un-promoted counterpart. Ti-CAT-II had the highest CH4 and CO2 conversion of about 55% and 64% respectively, while no reaction was observed for Ti-CAT-VI and Ti-CAT-IV. It can be inferred from the improved performance of the promoted catalysts that the promoters had a positive influence on the textural properties, metal support interaction and reduction behavior of the catalyst. These impacts of promoters were well shown by the characterization techniques used. From the thermogravimetric analysis, un-promoted catalyst gave the lowest carbon deposition. The promoted catalyst, especially by Ce, with higher amounts than 10% was found to have the highest carbon formation. This result implied that the promoters enhanced the activity performance of the catalyst, resulting in the formation of graphitic carbon, and hence, were not effective in boosting the stability via reduction of carbon deposition relative to the un-promoted catalyst. The TPO investigation indicated the types of carbon formed, which include atomic, amorphous, and graphitic carbon.

Ti-CAT-V was selected for further investigation at different GHSVs and subsequently at various CO2/CH4 ratios. An inverse relationship between GHSV and catalytic activity was observed. A GHSV of 19,500 feed flow rate mass of cat. - mL g· h and CO2/CH4 ratio of 0.5 gave the best results.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2073-4344/9/2/188/s1, Figure S1: XRD patterns of fresh catalysts.

**Author Contributions:** A.S.F., A.H.F, S.O.K., R.A. (Rasheed Alrasheed), R.A. (Rawan Ashamari) and A.B. carried out all experiments and characterization tests as well as shared in the analysis of the data and shared in the writing of the manuscript. A.S.F, S.O.K, A.E.A and A.B. wrote the paper and shared data analysis. A.H.F and A.A.I. contributed in writing the paper and edited it.

**Funding:** This research was funded by the Deanship of Scientific Research at King Saud University, Project No. RGP-119.

**Acknowledgments:** The authors would like to express their sincere appreciation to the Deanship of Scientific Research at King Saud University for its funding for this research group project No. (RGP-119).

**Conflicts of Interest:** The authors declare no conflict of interest.
