**4. Conclusions**

In summary, the combustion method was applied to prepare SiO2 supported Ni catalysts which showed remarkably smaller Ni nanoparticle sizes due to the synergistic effects of C2H5NO2 and NH4NO3 in the combustion process. This kind of Ni/SiO2 catalyst exhibits excellent coke-resistance performance and effectively suppresses the side reaction toward RWGS compared to that prepared with the conventional wetness impregnation method. As a result, there is almost no loss of activity with the H2/CO molar ratio close to the theoretical value at 1/1 after a 50-hour stability test over the Ni/SiO2-2/1 catalyst.

*Catalysts* **2019**, *9*, 183

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2073-4344/9/2/183/s1, Figure S1: XRD patterns of fresh Ni/SiO2 catalysts prepared with the combustion method by using different ratios of C2H5NO2 to NH4NO3, Figure S2: TEM images of spent Ni/SiO2-0/0 catalyst ((a) and (b)) and Ni/SiO2-2/1 catalyst ((c) and (d)) after 50-hours of reaction, Table S1: The equilibrium conversions of CH4 and CO2, H2/CO molar ratio, and selectivity to H2O calculated by HSC chemistry 6.0, Table S2: BET surface area of as-prepared Ni/SiO2 catalysts.

**Author Contributions:** Conceptualization, X.L. and Y.X. (Yan Xu); methodology, X.L., Y.X. (Yan Xu) and Q.L.; formal analysis, Y.X. (Yan Xu) and Q.L.; investigation, Y.X. (Yan Xu) and Q.L.; writing—original draft preparation, Y.X. (Yan Xu) and X.L.; writing—review and editing, B.L., F.J. and Y.X. (Yuebing Xu); funding acquisition, X.L.

**Funding:** This work is supported by the National Natural Science Foundation of China (21576119, 21878127), the Fundamental Research Funds for the Central Universities (JUSRP51720B, JUSRP11813), and the Program of Introducing Talents of Discipline to Universities (111 Project B13025).

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