Activity of zeolite catalysts

The activity of zeolite catalyst for the cracking of cumene was measured at several onstream periods at cumene flow rates of u = 0.01 mol/s and 0.32 mol/s (IECPDD 22 609, 1983). The results are tabulated. Taking the relation to be... 

Intraparticle diffusion can affect catalyst selectivity and activity. Similarly, intracrystalline diffusion can affect the selectivity and activity of zeolitic catalysts where intraparticle diffusion is negligible. Therefore, one... 

More recently it has been shown (21-24) that the equilibrated pH of the transition metal ion-exchange solution is also critical in determining the specific activity of zeolite catalysts. The results obtained for the CuY system (21) are shown in Fig. 8. 

An afterglow microwave plasma with stabilized pulse power was applied to the activation of zeolite catalysts for isobutane alkylation with butenes. It was found that the pretreatment of zeolite catalysts in a microwave plasma discharge affected their properties. The catalysts exhibited higher activity, stability in operation, and selectivity (the fraction of trimethylpentanes in the alkylate increased). The properties of catalysts after plasma activation depend on the treatment conditions such as plasma temperature and nonequilibrium character and depend only slightly on the initial activity of catalysts, which is primarily controlled by the catalyst preparation conditions. 

P-14 - Microwave plasma treatment as an effective technique for activation of zeolite catalysts... 

Olefin reactions were, among other reactions, also studied in situ by DRIFT spectroscopy as described in an review article by Maroni et al. [883], where a cell was used similar to that mentioned in Sect. 4.2 (cf. [176]). Salzer et al. [884] described in-situ DRIFT experiments of activation of zeolite catalysts, for instance, NH4-erionite, where they also employed the commercially available, heatable DRIFT cell mentioned in Sect. 4.2. 

Obtaining a reliable measure of the number of unpaired electrons ( spin concentration ) in a sample is often extremely useful. Even reliable relative values measured across a series of samples can often provide useful information. There are various important applications, as may be illustrated by the following incomplete list ESR dating, the determination of oxidized polycyclic aromatic hydrocarbons and of environmental carbon in samples of ambient air, the influence of air pollution (e.g., SO2 and NO2) on plants and soils, quantification of NO2, RO2, and HOI radicals in air samples, radiation dosimetry, redox activities of zeolite catalysts, and the metabolism of spin probes in cells and tissues. 

Dimethyl Ether Carbonylation. Contrary to low activity of zeolite catalysts in methanol carbonylation, H-MOR and H-FER has been shown to catalyze DME carbonylation to methyl acetate with the stable rates and >99% selectivity at 423-463 K after an initial induction period, during which acidic protons were replaced by methyl groups and co-produced water was removed (91,92). The rate of DME carbonylation was much higher than that for similar reactions of CH3OH, at least in part because H2 0 formed in parallel CH3OH dehydration reactions inhibits carbonylation steps (Table 22). 

The synthesis of ethylenediamine (EDA) from ethanolamine (EA) with ammonia over acidic t3pes of zeolite catalyst was investigated. Among the zeolites tested in this study, the protonic form of mordenite catalyst that was treated with EDTA (H-EDTA-MOR) showed the highest activity and selectivity for the formation of EA at 603 K, W/F=200 g h mol, and NH3/ =50. The reaction proved to be highly selective for EA over H-EDTA-MOR, with small amounts of ethyleneimine (El) and piperazine (PA) derivatives as the side products. IR spectroscopic data provide evidence that the protonated El is the chemical intermediate for the reaction. The reaction for Uie formation of EDA from EA and ammonia required stronger acidic sites in the mordenite channels for hi er yield and selectivity. 

Many of these problems disappeared in 1983 when Taramasso, Perego, and Notari synthesized titanium silicalite-1 (TS-1),1 which greatly affected the use of zeolite catalysts for practical oxidation chemistry. This catalyst shows outstanding activity, selectivity, and stability below 100°C. 

The transformation of n-hexadecane was carried out in a fixed-bed reactor at 220°C under a 30 bar total pressure on bifunctional Pt-exchanged HBEA catalysts differing only by the zeolite crystallites size. The activities of the catalysts and especially the reaction scheme depended strongly on the crystallites size. Monobranched isomers were the only primary reaction products formed with the smallest crystallites, while cracking was the main reaction observed with the biggest crystallites. This was explained in terms of number of zeolite acidic sites encountered by the olefinic intermediates between two platinum particles. 

The activity of the Pt-exchanged catalyst for n-C f, transformation increases when the crystallites size increases, which was totally unexpected. External diffusional limitations cannot be invoked since the size of the grains of catalyst is the same. Moreover, this would lead to the opposite result. Other experiments showed that the activity of zeolite-... 

The increasing volume of chemical production, insufficient capacity and high price of olefins stimulate the rising trend in the innovation of current processes. High attention has been devoted to the direct ammoxidation of propane to acrylonitrile. A number of mixed oxide catalysts were investigated in propane ammoxidation [1]. However, up to now no catalytic system achieved reaction parameters suitable for commercial application. Nowadays the attention in the field of activation and conversion of paraffins is turned to catalytic systems where atomically dispersed metal ions are responsible for the activity of the catalysts. Ones of appropriate candidates are Fe-zeolites. Very recently, an activity of Fe-silicalite in the ammoxidation of propane was reported [2, 3]. This catalytic system exhibited relatively low yield (maximally 10% for propane to acrylonitrile). Despite the low performance, Fe-silicalites are one of the few zeolitic systems, which reveal some catalytic activity in propane ammoxidation, and therefore, we believe that it has a potential to be improved. Up to this day, investigation of Fe-silicalite and Fe-MFI catalysts in the propane ammoxidation were only reported in the literature. In this study, we compare the catalytic activity of Fe-silicalite and Fe-MTW zeolites in direct ammoxidation of propane to acrylonitrile. 

An increased selectivity for phenol in the oxidation of benzene by H202 with TS-1 catalyst in sulfolane solvent was attributed to the formation of a bulky sulfolane-phenol adduct which cannot enter the pores of TS-1. Further oxidation of phenol to give quinones, tar, etc. is thus avoided. Removal of Ti ions from the surface regions of TS-1 crystals by treatment with NH4HF2 and H202 was also found to improve the activity and selectivity (227). The beneficial effects of removal of surface Al ions on the catalytic performance of zeolite catalysts for acid-catalyzed reactions have been known for a long time. 

Two points are emphasized (i) zeolites can be successfully operated at the same or higher severities (with respect to P/O (feed alkane/alkene) ratio and OS V (alkene space velocity)) than the liquid acids (ii) the productivities of zeolite catalysts (i.e., the total amount of alkylate produced per mass of catalyst) are roughly the same as of that of sulfuric acid. If the intrinsic activities of zeolites (which have 0.5-3 mmol of acid sites per gram) are compared with that of sulfuric acid (which has 20 mmol of acid sites per gram), zeolites outperform sulfuric acid. Nevertheless, the price of a zeolite catalyst and the high costs of... 

The applications of IR spectroscopy in catalysis are many. For example, IR can be used to directly characterize the catalysts themselves. This is often done in the study of zeolites, metal oxides, and heteropolyacids, among other catalysts [77,78], To exemplify this type of application, Figure 1.11 displays transmission IR spectra for a number of Co Mo O (0 < x < 1) mixed metal oxides with various compositions [79]. In this study, a clear distinction could be made between pure Mo03, with its characteristic IR peaks at 993, 863, 820, and 563 cm-1, and the Mo04 tetrahedral units in the CoMo04 solid solutions formed upon Co304 incorporation, with its new bands at 946 and 662 cm-1. These properties could be correlated with the activity of the catalysts toward carburization and hy-drodenitrogenation reactions. 

Figures 13 and 14 also show that hydrotreating the catalytic cracker feedstock increases the zeolite cracking. C3, and C5+ compounds are possible products of primary zeolite cracking. These figures show that hydrotreating of the feedstock results in larger yields of these primary cracking products and hence more valuable products. This improvement is most likely due to the heteroatom removal and the saturation of aromatic compounds during hydrotreating which tend to block active sites and reduce the activity of the catalyst.

Pilot unit tests have indicated that there is an upper limit for the zeolite to matrix surface area ratio (ZSA/MSA) for a residue catalyst. This observation was in contrast to the optimization study, which indicated that the ZSA/MSA should be as high as possible for maximum naphtha yield. An increase in the zeolite surface area is, according to the optimization study, expected to increase both the activity of the catalyst and its naphtha yield. But for catalysts with a high ZSA/MSA ratio, close to four or even higher, the observed naphtha yields have been lower than expected in the pilot unit tests, which indicate that there might be an upper limit for the ZSA/ MSA ratio in a residue application. 

As can be seen in Figure 4.8, the activity of the catalysts increased when the zeolite content of the catalyst increased. Since the matrix surface area was kept the same, the ZSA/MSA surface area ratio also increased. When comparing catalyst C-1 and catalyst C-2, the zeolite surface area was increased with 31 m /g, and the ZSA/MSA ratio increased from 2.5 to 3.5. As expected from our optimization studies, the activity for catalyst C-2 was significantly improved compared with catalyst C-1. The increase in activity was however not by far so pronounced for catalyst C-3, where the zeolite surface area was further increased with 21 m /g compared to catalyst C-2, which increased the ZSA/MSA surface area from 3.5 to 3.9. 

Recently, we reported that an Fe supported zeolite (FeHY-1) shows high activity for acidic reactions such as toluene disproportionation and resid hydrocracking in the presence of H2S [1,2]. Investigations using electron spin resonance (ESR), Fourier transform infrared spectroscopy (FT-IR), MiJssbauer and transmission electron microscopy (TEM) revealed that superfine ferric oxide cluster interacts with the zeolite framework in the super-cage of Y-type zeolites [3,4]. Furthermore, we reported change in physicochemical properties and catalytic activities for toluene disproportionation during the sample preparation period[5]. It was revealed that the activation of the catalyst was closely related with interaction between the iron cluster and the zeolite framework. In this work, we will report the effect of preparation conditions on the physicochemical properties and activity for toluene disproportionation in the presence of 82. ... 

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