Charakterisierung eines Trägerkatalysators durch effektive Diffusionskoeffizienten, Labyrinthfaktor und mittlere Porenradien

Synthesis of supported catalysts by impregnation and drying using aqueous chelated metal complexes

“…This last phenomenon highly affects the results of the drying process of impregnated supports. Not only is migration of the solvent to the external edge of the support particles suppressed, but also crystallization of a solid phase is avoided, due to which uniform distributions and high dispersions of the (precursor of the) active phase are favored [7,15,16]. We, therefore, propose that the beneficial effects of chelated metal precursors are based on two interdependent phenomena.…”

“…Since evaporation of the solvent takes place at the exterior of the support particles, capillary flow of solution to its exterior surface may take place, thereby causing production of so-called eggshell catalysts, often with a poor dispersion of the active phase. Pioneering work of Kotter and Riekert [7] has shown that an increase the viscosity of the impregnation solution suppresses outward flow of the solution and leads to more uniform activity profiles over support bodies. Alternative approaches involve very high or very low drying rates [2], but results are of moderate quality only.…”

How nitric oxide affects the decomposition of supported nickel nitrate to arrive at highly dispersed catalysts

“…8 g of PEO 20 PPO 70 PEO 20 (PEO = poly(ethylene oxide) and PO = poly(propylene oxide)) tri-block copolymer obtained from Aldrich was dissolved in 250 ml demineralized water of 40 • C. After the solution had become clear, 48 g of concentrated HCl (Merck) was added, followed by the addition of 21.5 ml of tetraethyl orthosilicate (Acros). Next, the mixture was stirred for 20 h at 40 • C after which it was transferred to an oven for further reaction at 80 • C for 48 h. The solid product was collected from the suspension by filtration, washing, drying in air for 12 h at 80 • C, and finally air calcination for 6 h at 550 • C. Davicat 1404SI silica gel (30-70 μm particles, total pore volume of 0.90 cm 3 g −1 and average pore diameter of 7 nm) was used as received from Grace-Davison.…”

“…In particular highly soluble nitrate salts are attractive as pure metal oxides can be obtained via facile and complete thermal decomposition in air. Regrettably, catalysts prepared as such often display poor metal dispersions, which has been ascribed to either redistribution during drying [15,[20][21][22][23] or to sintering during the air calcination [24][25][26][27][28] step. Using ordered mesoporous silica SBA-15 as model support, we recently reported for Ni and Co ex nitrate catalysts that this finds origin in severe sintering and redistribution during the air calcination treatment [29].…”