Controlling of physicochemical properties of nickel-substituted MCM-41 by adjustment of the synthesis solution pH and tetramethylammonium silicate concentration

The effect of initial synthesis solution pH and tetramethylammonium silicate concentration in the synthesis solution on the physical and chemical properties of MCM-41 was systematically investigated using N(2) physisorption, X-ray diffraction, temperature-programmed reduction, in situ Fourier transform IR, UV-vis, and X-ray absorption spectroscopies. pH and tetramethylammonium (TMA) fraction affect the porosity of MCM-41 and the reducibility of incorporated Ni cations; higher pH and TMA concentration produced more porosity with higher stability against reduction, which is attributed to more metal ions locating in the interior of the silica walls. The control of the pore diameter of mesoporous MCM-41 at the sub-nanometer scale may be accomplished by adjusting the pH and TMA fraction. pH may be used to control the surface free silanol group density and nickel reduction degree as well, and this is useful in the design of a specific catalyst for particular reactions, such as CO methanation, which requires highly dispersed, stable metallic clusters with controllable size.