(134a) A Novel Catalysts Preparation Method by Combustion Synthesis for Hydrogen Production From Oxidative Reforming of Methanol

Introduction: A novel method for catalysts synthesis, known as impregnated layer combustion synthesis (ILCS), is used to prepare catalysts for oxidative reforming of methanol. A description of the ILCS method and the evolution of catalysts is presented. Complex catalysts containing copper, zinc, zirconium and palladium were synthesized. These catalysts were characterized and their activity and selectivity for hydrogen production from oxidative reforming of methanol was measured. It is shown that the preparation procedures, including dispersion of Pd and the presence of ZrO2 support have significant effects on the catalytic behavior. Highly dispersed Pd catalysts were obtained by loading Pd over previously synthesized Cu/Zn/Zr based catalyst using a novel method, so-called, second wave impregnation (SWI). This method showed no significant effect on the catalyst structure but exceptional high activities for methanol conversion at low temperatures were achieved, giving 40% conversion at just 70 °C. Zirconia supported catalysts have high surface area but their catalytic performance is significantly affected by the presence of palladium. The catalysts promoted by, zirconia and palladium both, have high surface area and display superior selectivity toward hydrogen production over the whole range of investigated temperatures. Materials and Methods: Mixtures of metal nitrates Mec (NO3)c -yH2O (where Me = Cu, ZrO, Zn, or Pd) and glycine (as fuel) were used to synthesize catalysts in three modes of combustion synthesis techniques: volume combustion synthesis (VCS), impregnated layer combustion synthesis (ILCS), and a novel combination of the ILCS and VCS, so-called, second wave impregnation (SWI) approach. In the VCS method, a homogeneous solution was prepared by dissolving reactants in water. This solution was uniformly heated till it reaches the ignition temperature to start the combustion. In the ILCS method, a homogeneous solution of metal nitrates and fuel is impregnated in a cellulose paper which is dried at room temperature. This dried paper is ignited at one end to start the combustion reaction, which moves in a self sustained manner as a combustion front, leaving behind the final product of the required composition. In the SWI method, catalyst without Pd is prepared using ILCS and then the required amount of Pd is loaded on this catalyst using the VCS mode. Results and Discussion: Figure 1 shows the sequence of frames that illustrate the traveling of the combustion wave in smoldering mode, obtained by conventional digital (a) and high-speed IR (b) cameras. It can be seen that reaction front once initiated locally at one end is moving in a self sustained manner along the complex cellulose-reaction solution media. Visible light images taken by SONY camcorder (Fig.1a) undoubtedly reveal the existence of two reaction zones. The first front being darker in color than the non-reacted region is followed by an intense bright front with almost the same width (~10mm). The IR frames (Fig.1b) show that temperature of the first front is low (~300C), while the second front is relatively hot (>500°C). The various combustion synthesis modes of catalyst preparation were carefully studied by monitoring temperature distribution and combustion front movement using FLIR SC6000 IR camera. In order to study the phase transformations, samples were obtained from quenched areas in the two fronts, and were analyzed using XRD, SEM and EDS techniques. The temperature profile across the combustion front shows a sharp temperature gradient toward the product side, indicating a fast cooling of the products which prevents them from sintering and helps in making fine particles. SEM images obtained indicate particles as small as 10 nm. Final products are also being characterized by ICP-MS, XPS and EDS techniques.