Catalysts, general mixed

General procedure for Suzuki coupling. 4-Bromoanisole (125 pL, 1 mmol), phenylboronic acid (186 mg, 1.5 mmol), K2CO3 (0.55 g, 4 mmol) and the BaCei.j,Pdj,03.j, catalyst were mixed in a 20 ruL scintillation vial. A preheated 2-propanol/water solution (IPA/H2O, 1 1 v/v, 12 ruL, 80°C) was added, the vial was immediately placed on a hot plate stirrer and its temperature was maintained at (80 1) °C. The reaction mixture was stirred at 1000 rpm for 3 min, then cooled to room temperature. The 4-methoxybiphenyl product was extracted with diethyl ether (3 x 15 ruL). The organic fractions were washed with deionized water and dried with MgS04. After filtration, volatiles were removed under reduced pressure to yield the isolated product. 

Generally, variations of the chemical nature of the catalyst have not, so far, yielded as much information as have the systematic variations of the compositions of multicomponent catalysts. Most mixed catalysts in industry are heterogeneous mixtures. It would go beyond the scope of the present article to review them. But it is noticeable that, in general, two kinds of promoter action can be distinguished (1) Structural promotion in which the activation energy of the active constituent... 

Figure 7-4 Slurry reactor (left) for well-mixed gas-solid reactions and fluidized bed reactor (center) for liquid-solid reactions. At the right is shown a riser reactor in which the catalyst is carried with the reactants and separated and returned to the reactor. The slurry reactor is generally mixed and is described by the CSTR model, while the fluidized bed is described by the PFTR or CSTR models.

In general, mixed trimerization of isocyanates also gives mixtures (61JOC3334) however, it is possible to prepare isocyanurates of the type (157) from arenesulfonyl isocyanates in the presence of 1,2-dimethylimidazole as catalyst (76JOC3409). The mechanism is similar to that of the trimerization of isocyanates (Scheme 95). 

Among the more important catalysts are metals, which may be promoted by other metals, or by oxides and oxides, which are usually rendered more effective by mixing with other oxides. It is usual to distinguish between supported catalysts, generally metals in a finely divided condition on the surface of silicate minerals, and promoted catalysts, where an oxide, or occasionally some other compound, is mixed with the metal the mixture being sometimes also supported on an inert refractory support. The distinction is not, however, absolutely sharp. 

One-step partial oxidation of propane to acrylic acid (an essential chemical widely used for the production of esters, polyesters, amides, anilides, etc.) has been investigated so far on three types of catalysts, namely, vanadium phosphorus oxides, heteropolycompounds and, more successfully, on mixed metal oxides. The active catalysts generally consist of Mo and V elements, which are also found in catalysts used for the oxidation of propene to acrolein and that of acrolein to acrylic acid. 

Acrylonitrile is manufactured by passing propylene, ammonia, and air over a mixed-oxide catalyst at 400-500 C. The process is also a major source of acetonitrile and hydrogen cyanide which are obtained as the result of side reactions. Catalysts used in this process are generally mixed oxides of bismuth or antimony with other multivalent metals such as molybdenum, iron, uranium, and tin. At one time, the preferred catalyst for propylene... 

In the TA process, ethylene glycol and purified terephthalate acid are generally mixed in a ratio of less than 1.4 to 1 and heated in an initial phase with an antimony oxide catalyst to the boiling point of the ethylene glycol (198 °C). Because the reaction is relatively slow at this temperature, this step is often run under pressure to increase the achievable temperatures. As the reaction proceeds and the BHET is produced, the temperatures are Increased and the pressure is lowered to allow distillation of the evolved ethylene glycol. This phase resembles the PC step of the El process. 

CH4 reactions with CO2 or H2O on group VIII or noble metals (Ru, Rh, Pd, Ir, Pt) [1] form synthesis gas which is the precursor to valuable fuels and chemical compounds, as lirst shown by Fischer and Tropsch [2]. Due to the cost and availability of the nickel, compared to noble metals, Ni catalysts are used industrially. However, Ni-based catalysts tend to form inactive carbon residues that bloek the pores as well as the active sites of catalyst, and whose main activity is die formation of carbon filaments [3]. Therefore, the industrial methane steam reaction is usually performed under an excess of water to maintain the catalyst activity. Another alternative is the modification of the composition of the catalyst (generally Ni/Al203) by addition of a basic compound like MgO [4]. It is well known that the formation of NiO-MgO solid solution is easily favoured by calcining the mixed oxide at high temperatures [5] and much attention was devoted to its specific properties [6]. Parmaliana and al. 

In general, mixed-metal oxides are at present the most important catalytic system for the partial oxidation of C2-C5 alkanes into 0-containing partial oxidation products. However, different characteristics should be considered among the several catalysts within this group. For instance, VPO- and MoVO-based catalysts are the most effective systems for -butane (or -butene) oxidation to MA and propane (or propene) oxidation to acrylic acid, respectively. It must be indicated that, although some similarities are observed for the ammoxidation " over MoVO- or SbVO-based catalyts, the latter show very low selectivity during the partial oxidation of propane and no results with other alkanes have been reported. " Therefore, SbVO-based catalysts will not be explicitly included in the following discussion. 

It appears that Cu primarily provides electronic conductivity to the anode and is otherwise catalytically inert. This is confirmed by data showing that Au-ceria-SDC (samaria-doped ceria) composites exhibit a similar performance to that of Cu-ceria-SDC anodes, as Au would not be expected to add catalytic activity [86,87]. It is proposed that the function of ceria is primarily that of an oxidation catalyst, although mixed electronic-ionic conductivity (MEIC) could also enhance anode performance. In general, finely dispersed ceria seems more active than doped ceria ceramics, thus the redox oxygen exchange ability of ceria at fuel conditions might be considered as a key factor. 

ZnCr- and CuZnAl-LDOs. LDO catalysts generally give rise to high selectivity for methanol, while surface doping with Cs on mixed oxides increases catalyst stability (162,610-612). Higher alcohols can be also obtained with similar catalysts but at higher temperature and with a lower CO/H2 ratio (610,611). The doping of alkali, such as Cs, promotes the formation of branched alcohols (613). In addition, Ru supported on LDH-derived oxides, exhibits substantial selectivity toward alcohols, mainly methanol, at moderately low pressures (614). 

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