Acrolein catalytic selectivity

In contrast, with CO and H20 the aldehyde function of acrolein is selectively reduced to the alcohol function without reducing the C=C double bond by a catalytic system composed of Rh6(CO)16 and l,3-bis(dimethyl-amino)propane (80°C, 10 bar, 24 hr, yield 94%, CT 56) (315) ... 

Other important uses of stannic oxide are as a putty powder for polishing marble, granite, glass, and plastic lenses and as a catalyst. The most widely used heterogeneous tin catalysts are those based on binary oxide systems with stannic oxide for use in organic oxidation reactions. The tin—antimony oxide system is particularly selective in the oxidation and ammoxidation of propylene to acrolein, acryHc acid, and acrylonitrile. Research has been conducted for many years on the catalytic properties of stannic oxide and its effectiveness in catalyzing the oxidation of carbon monoxide at below 150°C has been described (25). 

Fig. 2. Left catalytic oxidation of C3 organic compounds over MgCr204. Conversion of propane A acetone X acrolein propene. Right catalytic oxidation of 2-propanol over MgCr204. conversion of 2-propanol selectivities to acetone A propene X COx-...

Mikroreaktoren sind so klein wie ein Fingerhut, Handdsblatt, May 1998 Steep progress in microelectronics, sensor and analytical techniques in the past transport intensification for catalysis first catalytic micro reactors available partial oxidation to acrolein partial hydrogenation to cyclododecene anodically oxidized catalyst supports as alternatives to non-porous supports study group on micro reactors at Dechema safety, selectivity, high pressure exclusion of using particle solutions limited experience with lifetime of micro reactors [236],... 

The Heck coupling reaction appeared to be a route of choice to achieve the synthesis of the modified-DIOP ligands. We previously studied the palladium-catalyzed coupling of acrolein and acrolein acetals with several polyaromatic and heteroaromatic bromides either in the presence of homogeneous or heterogeneous catalytic systems (6, 7). After optimization of the reaction conditions, high conversions and selectivities were achieved except with anthracenyl derivatives (8). Based on these results, we developed the synthesis of the desired ligands. The... 

A catalytic system Mo-V-Nb-W supported on alumina was prepared by impregnation and investigated for the selective oxidation of propane. The effects of the variation of each metal and of the catalyst preparation were analysed. The results show that Mo and V species supported on alumina can lead to catalysts with high selectivity to propene and reasonable selectivity to acrolein. The presence of Nb and W seems to have little effect. The catalyst can be affected by the method of impregnation. 

Theoretical calculations have also permitted one to understand the simultaneous increase of reactivity and selectivity in Lewis acid catalyzed Diels-Alder reactions101-130. This has been traditionally interpreted by frontier orbital considerations through the destabilization of the dienophile s LUMO and the increase in the asymmetry of molecular orbital coefficients produced by the catalyst. Birney and Houk101 have correctly reproduced, at the RHF/3-21G level, the lowering of the energy barrier and the increase in the endo selectivity for the reaction between acrolein and butadiene catalyzed by BH3. They have shown that the catalytic effect leads to a more asynchronous mechanism, in which the transition state structure presents a large zwitterionic character. Similar results have been recently obtained, at several ab initio levels, for the reaction between sulfur dioxide and isoprene1. ... 

Rhenium is one of the oxophilic atoms effective for oxidation reactions. ReOx species are likely to have chemical interaction with various oxide supports and exhibit unique catalytic properties that cannot be observed on monomeric rhenium oxides. A new active six-membered octahedral Re cluster in zeolite pores (H-ZSM-5 [HZ]) is produced from inactive [Re04] monomers in situ under selective propene oxidation to acrolein (C3H6+02 - CH2=CHCH0+H20) in the presence of ammonia that is not involved in the reaction equation [16], The cluster is transformed back to the original inactive monomer in the absence ammonia. Note that coexistence of spectator NH3 is indispensable for the selective oxidation. 

The CVD catalyst exhibits good catalytic performance for the selective oxidation/ammoxida-tion of propene as shown in Table 8.5. Propene is converted selectively to acrolein (major) and acrylonitrile (minor) in the presence of NH3, whereas cracking to CxHy and complete oxidation to C02 proceeds under the propene+02 reaction conditions without NH3. The difference is obvious. HZ has no catalytic activity for the selective oxidation. A conventional impregnation Re/HZ catalyst and a physically mixed Re/HZ catalyst are not selective for the reaction (Table 8.5). Note that NH3 opened a reaction path to convert propene to acrolein. Catalysts prepared by impregnation and physical mixing methods also catalyzed the reaction but the selectivity was much lower than that for the CVD catalyst. Other zeolites are much less effective as supports for ReOx species in the selective oxidation because active Re clusters cannot be produced effectively in the pores of those zeolites, probably owing to its inappropriate pore structure and acidity. 

The proposed Re6 cluster (8) with terminal and bridged-oxygen atoms acts as a catalytic site for selective propene oxidation under a mixture of propene, Oz and NH3. When the Re6 catalyst is treated with propene and Oz at 673 K, the cluster is transformed back to the inactive [Re04] monomers (7), reversibly. This is the reason why the catalytic activity is lost in the absence of ammonia (Table 8.5). Note that NH3, which is not involved in the reaction equation for the acrolein formation (C3H6+02->CH2=CHCH0+H20) is a prerequisite for the catalytic reaction as it produces the active cluster structure under the catalytic reaction conditions. 

The oxidation of propene to acrolein has been one of the most studied selective oxidation reaction. The catalysts used are usually pure bismuth molybdates owing to the fact that these phases are present in industrial catalysts and that they exhibit rather good catalytic properties (1). However the industrial catalysts also contain bivalent cation molybdates like cobalt, iron and nickel molybdates, the presence of which improves both the activity and the selectivity of the catdysts (2,3). This improvement of performances for a mixture of phases with respect to each phase component, designated synergy effect, has recently been attributed to a support effect of the bivalent cation molybdate on the bismuth molybdate (4) or to a synergy effect due to remote control (5) or to more or less strong interaction between phases (6). However, this was proposed only in view of kinetic data obtained on a prepared supported catalyst. 

One of the more successful conversions has been the selective oxidation of propylene to acrolein. In 1948, Hearne and Adams (7) reported that cuprous oxide produced acrolein from propylene with a yield of about 50% at propylene/oxygen ratios of about one. Even though the yield of acrolein was low, the search for improved catalytic systems provided few catalysts until the development of catalysts based on bismuth and molybdenum. 

The investigation of the mechanism of olefin oxidation over oxide catalysts has paralleled catalyst development work, but with somewhat less success. Despite extensive efforts in this area which have been recently reviewed by several authors (9-13), there continues to be a good deal of uncertainty concerning the structure of the reactive intermediates, the nature of the active sites, and the relationship of catalyst structure with catalytic activity and selectivity. Some of this uncertainty is due to the fact that comparisons between various studies are frequently difficult to make because of the use of ill-defined catalysts or different catalytic systems, different reaction conditions, or different reactor designs. Thus, rather than reviewing the broader area of selective oxidation of hydrocarbons, this review will attempt to focus on a single aspect of selective hydrocarbon oxidation, the selective oxidation of propylene to acrolein, with the following questions in mind ... 

To achieve selectivity in these reactions, a steric or electronic bias is required to favour one particular product or (more importantly given the reversible nature of CM) one metal-alkylidene precursor in the catalytic cycle.1 In particular, it has been known for some time that metathesis reactions involving one highly electron deficient olefin partner can be selective (for the first example using acrylonitrile or styrene and 1 see Ref. [40]) however,readily available potential substrates such as enones, acrylates and acrylamides are generally incompatible with either 1 or 2 (for two reported exceptions see Ref. [41]). This was partially overcome by the use of acrolein acetals as a,/i-unsaturated car-... 

Acrolein Zirconium and niobium mixed oxides have been shown to catalyze the dehydration of glycerol to acrolein, at 300°C in the presence of water with high selectivity (72%) at nearly total glycerol conversion [50]. Silica-supported niobia catalysts can also be used with similar catalytic performance [51]. Catalytic results for small-sized H-ZSM 5 zeolites showed that the high density of Bronsted acid sites favors acrolein production [52]. Acrolein production from glycerol has also been carried out in subcritical water at 360°C and 34 MPa with catalytic quantities of ZnS04 (791 ppm [g/g]) [52],... 

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