Catalysts alkaline earth metals

Processes rendered obsolete by the propylene ammoxidation process (51) include the ethylene cyanohydrin process (52—54) practiced commercially by American Cyanamid and Union Carbide in the United States and by I. G. Farben in Germany. The process involved the production of ethylene cyanohydrin by the base-cataly2ed addition of HCN to ethylene oxide in the liquid phase at about 60°C. A typical base catalyst used in this step was diethylamine. This was followed by liquid-phase or vapor-phase dehydration of the cyanohydrin. The Hquid-phase dehydration was performed at about 200°C using alkah metal or alkaline earth metal salts of organic acids, primarily formates and magnesium carbonate. Vapor-phase dehydration was accomphshed over alumina at about 250°C. 

Lewis acids, such as the haUde salts of the alkaline-earth metals, Cu(I), Cu(II), 2inc, Fe(III), aluminum, etc, are effective catalysts for this reaction (63). The ammonolysis of polyamides obtained from post-consumer waste has been used to cleave the polymer chain as the first step in a recycle process in which mixtures of nylon-6,6 and nylon-6 can be reconverted to diamine (64). The advantage of this approach Hes in the fact that both the adipamide [628-94-4] and 6-aminohexanoamide can be converted to hexarnethylenediarnine via their respective nitriles in a conventional two-step process in the presence of the diamine formed in the original ammonolysis reaction, thus avoiding a difficult and cosdy separation process. In addition, the mixture of nylon-6,6 and nylon-6 appears to react faster than does either polyamide alone. 

Silver alone on a support does not give rise to a good catalyst (150). However, addition of minor amounts of promoter enhance the activity and the selectivity of the catalyst, and improve its long-term stabiHty. Excess addition lowers the catalyst performance (151,152). Promoter formulations have been studied extensively in the chemical industry. The most commonly used promoters are alkaline-earth metals, such as calcium or barium, and alkaH metals such as cesium, mbidium, or potassium (153). Using these metals in conjunction with various counter anions, selectivities as high as 82—87% were reported. Precise information on commercial catalyst promoter formulations is proprietary (154—156). 

A number of basic materials such as hydroxides, hydrides and amides of alkaline and alkaline earth metals and metal oxides such as zinc oxide and antimony oxide are useful catalysts for the reaction. Acid ester-exchange catalysts such as boric acid, p-toluene sulphonic acid and zinc chloride are less... 

The heavier alkaline earth metals Ca, Sr, Ba (and Ra) react even more readily with non-metals, and again the direct formation of nitrides M3N2 is notable. Other products are similar though the hydrides are more stable (p. 65) and the carbides less stable than for Be and Mg. There is also a tendency, previously noted for the alkali metals (p. 84), to form peroxides MO2 of increasing stability in addition to the normal oxides MO. Calcium, Sr and Ba dissolve in liquid NH3 to give deep blue-black solutions from which lustrous, coppery, ammoniates M(NH3)g can be recovered on evaporation these ammoniates gradually decompose to the corresponding amides, especially in the presence of catalysts ... 

Alkaline earth metals in general, and sodium in particular, are detrimental to the FCC catalyst. Sodium permanently deactivates the catalyst by neutralizing its acid sites. In the regenerator it causes the zeolite to collapse, particularly in the presence of vanadium. Sodium comes from two prime sources ... 

Tabushi, I. Yamamura, K. Water Soluble Cyclophanes as Hosts and Catalysts, 113,145-182 (1983). Takagi, M., and Ueno, K. Crown Compounds as Alkali and Alkaline Earth Metal Ion Selective Chromogenic Reagents. 121, 39-65 (1984). 

Ca3(BN2)2 is readily formed when (distilled) calcium metal is melted in the presence of (layer-type) boron nitride. This reaction provides some insight on how alkaline-earth metals like calcium may act as a catalyst in the phase transformation of layered a-BN into its cubic modification. Instead of metals, nowadays alkaline-earth (Ca, Sr, Ba) nitridoborates can be used as a flux catalyst in high-pressure and high-temperature transformation reactions to produce cubic boron nitride [15]. 

The large amounts of natural gas (mainly methane) found worldwide have led to extentive research programs in the area of the direct conversion of methane [1-3]. Ihe oxidative transformation of methane (OTM) is an important route for the effective utilization of the abundant natural gas resources. How to increase catalyst activity is a common problem on the activation of methane. The oxidation of methane over transition m al oxides is always high active, but its main product is CO2, namely the product of deep oxidation. It is because transition metal oxides have high oxidative activity. So, they were usually used as the main corrqtonent of catalysts for the conqilete oxidation of alkane[4]. The strong oxidative activity of CH4 over tran on metal oxides such as NiO indicates that the activation of C-H bond over transition metal oxides is much easier than that over alkaline earth metal oxides and rare earth metal oxides. Furthermore, the activation of C-H bond is the key step of OTM reaction. It is the reason that we use transition metal oxides as the mam conq>onent of the OTM catalysts. However, we have to reahze that the selectivity of OTM over transition metal oxides is poor. 

Over An deposited on 3-D mesoporous Ti-Si02 with pore diameter of 9nm, one of the best results was obtained. At an SV of 4000 h/mL/g-cat., propylene conversion above 8%, PO selectivity of 91% giving a steady STY of 80 g PO/h/kg-cat. [84]. The surfaces of 3-D mesoporous Ti-Si02 were trimethylsilylated for rendering hydro-phobicity, which enables higher temperature operation of reaction [86]. As a solid phase promoter, alkaline or alkaline earth metal chlorides are efficient, however, chloride anions markedly enhance the coagulation of An particles in a short period [87]. Finally, Ba(N03)2 was selected as the best promoter which might kill the steady acid sites as BaO (after calcination) on the catalyst surfaces [84,88]. 

Tanoka, T., Yokata, K., Doi, H. et al. (1997) Selective catalytic reduction of NO over PtMo catalysts with alkaline or alkaline earth metal under lean static conditions, Chem. Lett. 409. 

This is a quite remarkable result, as the chemoselective hydrogenation of geraniol over a heterogeneous catalyst has rarely been reported. It can be carried out over platinum containing zeolite (9), over Pt/Al203 modified with carboxylic acids (10), over Ni/diatomaceous earth and alkali hydroxides or carbonates (11) or NiRaney and alkali or alkaline earth metal hydroxides (12), yields never exceeding 85%. 

Fig. 14. CH4 conversion (a) and CO yield (b) in the C02 reforming of CH4 catalyzed by reduced 16.7-wt% NiO/alkaline earth metal oxides. Before reaction, each catalyst was reduced in flowing H2 at 773 K for 14 h. Reaction conditions pressure, 1 atm temperature, 1063 K feed gas molar ratio, CH4/C02 = 1/1 GHSV, 60,000 mL (g catalyst)-1 h-1 (239).

Biodiesel is a mixture of methyl esters of fatty acids and is produced from vegetable oils by transesterification with methanol (Fig. 10.1). For every three moles of methyl esters one mole of glycerol is produced as a by-product, which is roughly 10 wt.% of the total product. Transesterification is usually catalyzed with base catalysts but there are also processes with acid catalysts. The base catalysts are the hydroxides and alkoxides of alkaline and alkaline earth metals. The acid catalysts are hydrochloride, sulfuric or sulfonic acid. Some metal-based catalysts can also be exploited, such as titanium alcoholates or oxides of tin, magnesium and zinc. All these catalyst acts as homogeneous catalysts and need to be removed from the product [16, 17]. The advantages of biodiesel as fuel are transportability, heat content (80% of diesel fuel), ready availability and renewability. The... 

In the fatty acid distillation process, wastewater is generated as a result of an acidification process, which breaks the emulsion. This wastewater is neutralized and sent to the sewer. It will contain salt from the neutralization, zinc and alkaline earth metal salts from the fat splitting catalyst, and emulsified fatty acids and fatty acid polymers. 

Similarly, CALB has been used in combination with a palladium/alkaline earth metal-based racemization catalyst to effect a DKR on the benzylic amine 56e (Scheme 2.27). The (R)-amide 57e was obtained in very good yield and excellent optical purity. Several other substrates also underwent the reaction [29],... 

This review is a summary of the work done and potential opportunities for inexpensive and easily accessible base catalysts, such as alkaline earth metal oxides and hydroxides, as well as alkali metals and oxides supported on alkaline earth metal oxides. Preparation methods of these materials, as well as characterization of basic sites are reported. An extensive review of their catalytic applications for a variety of organic transformations including isomerization, carbon-carbon and carbon-oxygen bond formation, and hydrogen transfer reactions is presented. 

Concerning the nature of Lewis basic sites, little work has been done to establish general rules and models, except for alkaline earth metal oxides and zeolites. With respect to the former, i.e., the nature of oxygen Lewis basic sites on alkaline earth metal oxide catalysts, a charge-density model predicts that the strength of the sites decreases in the order > OH > H2O > H30. ... 

The most general methodology followed to prepare alkaline earth metal oxides as basic catalysts consists of the thermal decomposition of the corresponding hydroxides or carbonates in air or under vacuum. Decomposition of hydroxides is frequently used to prepare MgO and CaO, whereas BaO and SrO are prepared from the corresponding carbonates as precursor salts. Preparation of alkaline earth metal... 

Adsorption of a specific probe molecule on a catalyst induces changes in the vibrational spectra of surface groups and the adsorbed molecules used to characterize the nature and strength of the basic sites. The analysis of IR spectra of surface species formed by adsorption of probe molecules (e.g., CO, CO2, SO2, pyrrole, chloroform, acetonitrile, alcohols, thiols, boric acid trimethyl ether, acetylenes, ammonia, and pyridine) was reviewed critically by Lavalley (50), who concluded that there is no universally suitable probe molecule for the characterization of basic sites. This limitation results because most of the probe molecules interact with surface sites to form strongly bound complexes, which can cause irreversible changes of the surface. In this section, we review work with some of the probe molecules that are commonly used for characterizing alkaline earth metal oxides. 

Alkaline earth metal oxides have been used as solid base catalysts for a variety of organic transformations. Excellent reviews by Tanabe 4) and Hattori 2,3,7) provide detailed information about the catalytic behavior of alkaline earth metal oxides for several organic reactions of importance for industrial organic synthesis. In this section, we describe in detail reactions that have been reported recently to be catalyzed by alkaline earth metal oxides. 

Alkaline earth metal oxides are active catalysts for double bond isomerization. For example, SrO exhibits high activity and selectivity for the isomerization of a-pinene to /1-pinene 110). MgO and CaO have excellent activities for isomerization of 1-butene and 1,4-pentadiene and, particularly, for isomerization of compounds containing heteroatoms, such as allylamine or 2-propenyl ethers 111-115). Recently... 

Baba and Endou 117) reported that CaO is an active catalyst for isomerization of VBH to EBH when it is evacuated at temperatures above 800 K, whereas MgO did not show any activity for this process. However, some discrepancies have been reported by Kabashima et al. 10), who found that MgO, CaO, SrO, and BaO catalyze the isomerization of VBH to EBH, with the order of activity being CaO > MgO > SrO > BaO. This order in activity is attributed to the trends in base strength of oxides (BaO > SrO > CaO > MgO) and the surface area, the latter decreasing in the order MgO > CaO > SrO > BaO (Table II). The activity of the CaO was the highest among these alkaline earth metal oxides, and the activity of the MgO varied with the pre-treatment temperature, reaching a maximum it was 873 K ... 

Results Characterizing Isomerization of VBH to EBH on Alkaline Earth Metal Oxide Catalysts in a... 

Several cross-aldol condensations have been performed with alkaline earth metal oxides, including MgO, as a base catalyst. A general limitation of the cross-aldol condensation reactions is the formation of byproducts via the self-condensation of the carbonyl compounds, resulting in low selectivities for the cross-aldol condensation product. For example, the cross-condensation of heptanal with benzalde-hyde, which leads to jasminaldehyde (a-K-amylcinnamaldehyde), with a violet scent... 

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