Catalyst acidity-basicity

Idem, R.O., Katikaneni, S.P.R., Bakhshi, N.N., 1997. Catalytic conversion of canola oil to fuels and chemicals roles of catalyst acidity, basicity and shape selectivity on product distribution. Fuel Processing Technology 51 (1—2), 101—125. 

The presence of increased basic nitrogen compounds, such as pyridines and quinoline in the FCC feedstock, also attack catalyst acid sites. The result is a temporary loss of catalyst activity and a subsequent increase... 

Basic Nitrogen is the nitrogen compounds in the FCC feed that react with the catalyst acid sites, thereby reducing the catalyst s activity and selectivity. 

The decarbonylation of aromatic aldehydes with sulfuric acid" is the reverse of the Gatterman-Koch reaction (11-16). It has been carried out with trialkyl- and trialkoxybenzaldehydes. The reaction takes place by the ordinary arenium ion mechanism the attacking species is H and the leaving group is HCO, which can lose a proton to give CO or combine with OH from the water solvent to give formic acid." Aromatic aldehydes have also been decarbonylated with basic catalysts." When basic catalysts are used, the mechanism is probably similar to the SeI process of 11-38. See also 14-39. 

For the studied catechol methylation reaction the catalyst structure and surface properties can explain the catalytic behaviour As mentioned above, the reaction at 260-350°C has to be performed over the acid catalysts. Porchet et al. [2] have shown, by FTIR experiments, the strong adsorption of catechol on Lewis acid/basic sites of the Y-AI2O3 surface. These sites control the reaction mechanism. 

Due to the formation of Ca/Al mixed oxide on the surface, the Ca -modified alumina has a completely different structure compared to the spinel one This leads to a different type of surface Lewis acid/basic sites, rendering the catalyst 30 times less active. 

Since formation of citraconic anhydride from pyruvic acid is one of "acid to acid type" transformations, such as reactions from isobutyric acid to methacrylic acid and from lactic acid to pyruvic acid, the required catalysts must be acidic [11). If the catalysts are basic, it may be impossible to obtained acidic products, because basic catalysts activate selectively acidic molecules and, as a result, they show a very high activity for the decomposition of acidic products [11]. 

In applications where Nafion is not suitable, at temperatures above 200 °C with feed gas heavily contaminated with CO and sulfur species, a phosphoric acid fuel cell (PAFC)-based concentrator has been effective [15]. Treating the gas shown in Table 1, a H2 product containing 0.2% CO, 0.5%CO2 and only 6 ppm H2S was produced. The anode electrode was formed from a catalyst consisting basically of Pt-alloy mixed with 50% PTFE on a support of Vulcan XC-72 carbon. The cathode was... 

Mg/Me (Me=Al, Fe) mixed oxides prepared from hydrotalcite precursors were compared in the gas-phase m-cresol methylation in order to find out a relationship between catalytic activity and physico-chemical properties. It was found that the regio-selectivity in the methylation is considerably affected by the surface acid-basic properties of the catalysts. The co-existence of Lewis acid sites and basic sites leads to an enhancement of the selectivity to the product of ortho-C-alkylation with respect to the sole presence of basic sites. This derives from the combination of two effects, (i) The H+-abstraction properties of the basic site lead to the generation of the phenolate anion, (ii) The coordinative properties of Lewis acid sites, through their interaction with the aromatic ring, make the mesomeric effect less efficient, with predominance of the inductive effect of the -O species in directing the regio-selectivity of the C-methylation into the ortho position. 

The scheme also indicates that high glyceric acid selectivity is obtainable either via a selective catalyst for glyceraldehydes formation, or with a less selective catalyst in basic medium, where the hydroxyacetone-glyceric aldehyde equilibration is established. 

During the first decade when solid-phase synthesis was executed using Fmoc/tBu chemistry, the first Fmoc-amino acid was anchored to the support by reaction of the symmetrical anhydride with the hydroxymethylphenyl group of the linker or support. Because this is an esterification reaction that does not occur readily, 4-dimethylaminopyridine was employed as catalyst. The basic catalyst caused up to 6% enantiomerization of the activated residue (see Section 4.19). Diminution of the amount of catalyst to one-tenth of an equivalent (Figure 5.21, A) reduced the isomerization substantially but did not suppress it completely. As a consequence, the products synthesized during that decade were usually contaminated with a small amount of the epimer. In addition, the basic catalyst was responsible for a second side reaction namely, the premature removal of Fmoc protector, which led to loading of some dimer of the first residue. Nothing could be done about the situation,... 

Reaction conditions were as follows reaction temperature = 863 K contact time 3 sec CH4 02 molar ratio = 11. A, B and I refer to acid, basic and intermediate AHM impregation pH media, respectively. Notice that 0.8 Mo nm-2 is common for the two catalysts series. Reactor 2. 

With tin vanadates, the selectivity for the formation of butadiene goes through a maximum at an atomic ratio Sn/V = 9. Below this ratio, the acidity is greater, leading to more maleic acid anhydride in the reaction products. Butadiene will adsorb more with increasing acidity and will have a greater opportunity to be oxidized. The resulting acid anhydride will desorb relatively easily from an acid catalyst. A basic catalyst will result in more combustion products. 

This somewhat simplified picture of possible transitions from one mechanism to another can be expanded and supplemented by a finer differentiation of the factors influencing bond strength and catalyst acid-base properties. Such structural parameters are the number and nature of substituents on Ca and Cp and the nature of the group X. The action of a catalyst depends on its cation charge and radius, on anion basicity and on lattice and surface arrangement (for some details see ref. 67). A temperature increase usually shifts the mechanism in the direction of El. 

Unlike to zeolite catalysts acidic sites hardly play any role in the C-methylation of 2-Et-A on oC-Fe Oj or GeOg-FegO since germanium promotion induces a considerable increases in the 2-Et-6-Me-A yield and selectivity while acidity remains practically unchanged. Regarding that the yield of the N-alkyl derivatives is only slightly influenced by germanium the participation of the weak basic or acidic sites in the N-methylation can not be ruled out. 

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