## 2 Materials and Methods  
For a total solid mass of 14 g, 66.7% of nickel nitrate hexahydrate and 50% glycine were mixed with various quantities of water (25, 50, 75, 100 mL) and eight solutions were prepared--two for each quantity of water. One solution from each water quantity was preheated in a borosilicate glass beaker on a hot plate with mild magnetic stirring until the temperature reached 70 \({}^{\circ}\)C. At that point, the beaker was placed in a preheated furnace at 500 \({}^{\circ}\)C in air atmosphere for the SCS to take place. The other four solutions (with 25, 50, 75, and 100 mL of water) were placed directly in the furnace without any pretreatment. In all experiments, after the completion of the SCS cascade of reactions, the beaker was removed from the furnace and left to cool down to room temperature. In Table 1 that follows, the materials that have been used for catalysts production using Solution Combustion Synthesis (SCS) are listed. Also, the manufacturers and their assay are included. The microstructural properties of the synthesized catalysts were determined by several methods. Atomic structure was determined by X-ray diffraction measurements in a Siemens Spellman DF3 spectrometer with Cu-K\(\alpha\) radiation. For the semi-quantitative XRD analysis, 10% KCl was added in all samples as an internal standard. By normalizing the XRD results against the 10% KCl internal standard and calculating the peak ratio of intensities of particular peaks (ensuring that they were unique for each phase being analyzed), it was possible to determine the relative content of each phase in the material. The hkl of the peaks selected for each phase were: 111 for nickel, 101 for nickel oxide, and 100 for potassium chloride. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Material** & **Manufacturer** & **Assay/Purity** \\ \hline Nickel (II) nitrate hexahydrate for analysis & & \\ [Ni(NO\({}_{3}\))\({}_{2}\):6H\({}_{2}\)O] & Merck (Darmstadt, Germany) & 99.0–102.0\% \\ Glycine for synthesis [CH\({}_{2}\)NH\({}_{2}\)COOH] & PanReacAppliChem (Darmstadt, Germany) & 99.0 \% \\ Maleic acid [HOOCCH=CHCOOH] & Riedel-de Haën (Bucharest, Romania) & 99.0 \% \\ Hydrogen [H\({}_{2}\)] & Air liquide (Paris, France) & 99.999\% \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Materials used for SCS catalysts production and the hydrogenation reaction. Determination of the temperature and velocity of the combustion wave during SCS was carried out using three 100 \(\upmu\)m diameter K-type (chromel-alumel) thermocouples placed in and above the solution. A PICO TC-08 conditioner was used to convert, filter, and amplify the temperature signals, which were recorded at a rate of 0.5 ms. The installation has been manufactured in the Advanced Ceramics & Composite Materials Laboratory of NCSR \"Demokritos\" (Athens, Greece). No attempt was made to move the thermocouples since these measurements were used only to pinpoint the reaction time and correlate it to the appearance of the combustion phenomena. In any case, this work is being extended in order to compare the measured reaction temperatures with calculated adiabatic reaction temperatures, and will be published in future work. The temperature of the combustion wave was also measured in situ using a high-speed infrared (IR) camera (FLIR Systems, model A655 SC, Wilsonville, Oregon, United States). The speed of the combustion wave was calculated by analysis of the data obtained from the high-speed infrared camera. BET (Brunauer, Emmett and Teller) specific surface area and pore distribution measurements were carried out in a GAPP V-Sorb 2800 analyzer (Beijing, China) using nitrogen (99.9%) with helium (99.999%) as the carrier gas. All samples were subjected to degassing under vacuum (3\(\cdot\)10\({}^{-4}\) Torr) in two stages during pretreatment. During the first stage the samples were heated up to 80 \({}^{\circ}\)C for 45 min, while in the second stage they were heated up to 150 \({}^{\circ}\)C for another 45 min.