Acid-base synergistic effect

This kind of acid-base synergistic effect relates with the precursor of catalysts (to be expressed by Fe +/Fe +), but not directly with the absolute amounts of acidic ad basic oxides. It can be seen from Fig. 3.39 that the ratio of acid and base surface area of the highest active catalyst is about 1.1 and the catalyst precursor phase is... 

The synthetic route to the structurally related bis-thioureas of type 32 from (R)-5,5, 6,6, 7,7, 8,8 -octahydro-l,T-binaphthyl-2,2 -diamine was reported by Shi. The effectiveness of the acid-base synergistic catalysis of parent 32a and N,N-diisopropylethylamine was verified by application to the asymmetric Henry reaction of nitromethane with aromatic aldehydes (Scheme 7.57) [86]. Moreover, the Morita-Bayhs-Hillman reaction between 2-cyclohexen-l-one or 2-cyclopenten-1-one and aromatic aldehydes was found to proceed with moderate to good levels of enantioselectivity under the catalysis of 32b, which has additional 3,5-bis(trifluoromethyl)phenyl groups at the 3,3 -positions of the octahydrobinaph-thyl backbone, and l,4-diazabicyclo[2.2.2]octane (DABCO) (Scheme 7.57) [87]. 

We expected to control the direction of OTM reaction over NiO by sur ce modification, namely making use of the interaction between NiO and other conq>onents to beget a synergistic effect. In this paper, two completely different behaviors of the oxidative transformation of methane were performed over the nickel-based catalysts because of the different modifications by alkali metal oxide and rare earth metal oxide and the different interactions between nickel and supports. Furthermore, the two completely different reactions were related with the acid-base properties of catalysts and the states of nickel present. 

Another interesting feature of the AMO photocatalysts is the effect of diluent substrates such as MgO or activated C. Addition of substrates causes an increase in the rate of photoassisted catalytic oxidation of isopropanol. A synergistic effect is clear specific amounts of diluent lead to an increase. Too much or too little diluent leads to a decrease in rate. The exact explanation of this synergistic effect is not known, however, it may related to the ability of species such as OH or adsorbed hydrocarbons and intermediates to travel back and forth across the AMO/substrate interface. There does not seem to be a correlation of rate with the surface area, acid base character, particle size or other physical/chemical properties of the substrate. 

The mechanism of action could be as follows the sandpaper abrasion and acid have a synergistic effect of physical and chemical resurfacing that improves the quality of the entire epidermis (Figure 21.1). When the post-peel cream penetrates the atrophic base of the stretch marks, it causes inflammation (controlled by the antioxidants) that stimulates fibroblast proliferation and metabolic production of the non-cellular components of the dermis (Figure 21.2). 

Recent developments in the design and application of supported reagent catalysts offer considerable potential for clean synthesis. Synergistic effects between the support material and the reagent can lead to unexpectedly high activity. Thus "clayzic" is a potent solid acid catalyst for certain Friedel-Crafts reactions despite the low activity of the individual components. This and other similar clay and silica-based solid acid catalysts have been shown to have many useful applications in liquid phase reactions and some of them have been commercialised as environmentally friendly replacements for conventional acidic reagents. ... 

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