*3.1. Catalyst Preparation*

The supported Ni catalysts were prepared with SiO2 support (Tosoh Kabushiki-gaisha, Tokyo, Japan) by the combustion method, and the combustible materials contained hydrate glycine (C2H5NO2), ammonium nitrate (NH4NO3) and nickel nitrate (Ni(NO3)2·6H2O) with different C2H5NO2/Ni(NO3)2·6H2O and NH4NO3/Ni(NO3)2·6H2O molar ratios. Briefly, the aqueous solution of the desired amounts of C2H5NO2, NH4NO3 and Ni(NO3)2·6H2O was added into the SiO2 support at room temperature by incipient wetness impregnation, followed by drying with a rotary evaporator for 2 hours at 80 ◦C, and then overnight at 120 ◦C. Afterwards, the dried solid materials were calcined

in air for 1 hour at 300 ◦C with a heating rate of 1 ◦C/min and another 3 hours at 550 ◦C with a heating rate of 2 ◦C/min. The calcined samples were denoted as Ni/SiO2-x/y, where x and y indicate the molar ratio of C2H5NO2/Ni(NO3)2·6H2O and NH4NO3/Ni(NO3)2·6H2O, respectively. The metallic Ni loading was 10 wt%. The samples were then crushed and sieved into a 40–60 mesh size for subsequent catalytic tests.
