Strong oxide-oxide interactions in silica-supported magnetite catalysts. 2. The core/shell nature of the interaction

Coverage of palladium by silicon oxide during reduction in H2 and complete oxidation of methane

“…Similar effects on other metals and oxides have been reported before [10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Reduction of Pd/SiO 2 in H 2 at a temperature above 723 K could form palladium silicides, such as Pd 2 Si [10], Pd 3 Si [11,12,21], Pd 4 Si [12,21], with the type of silicide formed depending on the reduction conditions.…”

“…Lund and Dumesic [16] explained the migration of silica on Fe 3 O 4 by Si 4+ substitution into the tetrahedral sites of Fe 3 O 4 and displacement of Fe 3+ to adjacent octahedral sites, which occurred over the entire surface of Fe 3 O 4 , rather than being confined to the interface. The substituted Fe 3 O 4 retained 80% capacity to adsorb NO but showed one order of magnitude lower turnover rate for water-gas shift reactions because there were still octahedrally coordinated iron cations on the surface that could adsorb NO but this compound was not active for catalytic reaction.…”

“…Silica migration was observed on an iron oxide/silica model catalyst at 670 K on treatment in H 2 O/CO or H 2 O/H 2 gas mixture, but was not observed on treatment in CO 2 /CO or O 2 [14]. After treating a silica-supported magnetite catalyst in a water-containing environment at 650 K and near-atmospheric pressure, the apparent turnover rate for water-gas shift was reduced by approximately one order of magnitude, although the capacity to chemisorb NO did not diminish significantly [15,16]. Muto et al [17,18] tested Pd/SiO 2 , Pd/Al 2 O 3 , and Pd/SiO 2 -Al 2 O 3 catalysts for methane oxidation.…”

Structure and Fischer–Tropsch performance of iron–manganese catalyst incorporated with SiO2

“…For the high temperature reduction region, the reduction temperature decreases with the increase of SiO 2 , and the amount of hydrogen-consumed decreases with the increase of SiO 2 content. It has been reported that K 2 O could restrain the reduction of iron oxide due to the interaction between K 2 O and iron oxide [10,32,33], which could suppress the adsorption of hydrogen on catalyst surface and therefore restrain the reduction of iron oxide that underlies and/or neighbors potassium promoter [8,10]. The addition of SiO 2 decreases the amount of the effective potassium, and favors the reduction of FeO.…”

Effect of K promoter on the structure and catalytic behavior of supported iron-based catalysts in fischer-tropsch synthesis

“…Total reduction of all catalysts was observed below 800 This decrease may be the result of an interaction between potassium oxide, copper oxide and iron oxide. A strong interaction of potassium oxide with iron oxide may suppress the adsorption of hydrogen on the catalyst surface and impede the reduction of iron oxide adjacent to the potassium promoter (Lund and Dumesic, 1982;Rankin and Bartholomew, 1986). The increase in α-Fe 2 O 3 crystallite size decreased the surface area for contact with the reductant H 2 and may have contributed to the reduction phenomenon observed in the TG analysis.…”