Dehydrogenation Of N-dodecane Research Articles

Active, selective and stable Pt/Fe-silicalite-1 catalyst for dehydrogenation of n-dodecane to linear mono-dodecene

Dehydrogenation of n-dodecane to linear mono-dodecene by traditional Pt-Sn/γ-Al2O3 catalyst suffers from low linear mono-dodecene selectivity and catalyst instability due to the surface acidity of γ-Al2O3. In this work, we used Fe-silicalite-1, ZSM-5 and silicalite-1 as supports to disperse Pt for catalyzing n-dodecane dehydrogenation. Various characterization of Pt/zeolite catalysts confirm that metallic Pt donating electrons to Fe3+ in Pt/Fe-silicalite-1 catalyst makes Pt nanoparticles anchored at the framework Fe site in the Fe-silicalite-1 zeolite, which leads to formation of well-dispersed and high stability of Pt nanoparticles. Meanwhile, the acidity of as-prepared catalysts follows the order of Pt/ZSM-5 > Pt/Fe-silicalite-1 > Pt/silicalite-1. The higher catalytic activity, higher linear mono-dodecene selectivity and superior stability of Pt/Fe-silicalite-1 catalyst compared to Pt/ZSM-5 and Pt/silicalite-1 catalysts for n-dodecane dehydrogenation is owing to well-dispersed and stable electron-deficient metallic Pt anchored at the Fe site in Fe-silicalite-1 zeolite framework and moderate acidity of Fe-silicalite-1.

β-Hydride Elimination and C-H Activation by an Iridium Acetate Complex, Catalyzed by Lewis Acids. Alkane Dehydrogenation Cocatalyzed by Lewis Acids and [2,6-Bis(4,4-dimethyloxazolinyl)-3,5-dimethylphenyl]iridium.

NaBArF4 (sodium tetrakis[(3,5-trifluoromethyl)phenyl]borate) was found to catalyze reactions of (Phebox)IrIII(acetate) (Phebox = 2,6-bis(4,4-dimethyloxazolinyl)-3,5-dimethylphenyl) complexes, including (i) β-H elimination of (Phebox)Ir(OAc)(n-alkyl) to give (Phebox)Ir(OAc)(H) and the microscopic reverse, alkene insertion into the Ir-H bond of (Phebox)Ir(OAc)(H), and (ii) hydrogenolysis of the Ir-alkyl bond of (Phebox)Ir(OAc)(n-alkyl) and the microscopic reverse, C-H activation by (Phebox)Ir(OAc)(H), as indicated by H/D exchange experiments. For example, β-H elimination of (Phebox)Ir(OAc)(n-octyl) (2-Oc) proceeded on a time scale of minutes at -15 °C in the presence of (0.4 mM) NaBArF4 as compared with a very slow reaction at 125 °C in the absence of NaBArF4. In addition to NaBArF4, other Lewis acids are also effective. Density functional theory calculations capture the effect of the Na+ cation and indicate that it operates primarily by promoting κ2-κ1 dechelation of the acetate anion, which opens the coordination site needed to allow the observed reaction to proceed. In accord with the effect on these individual stoichiometric reactions, NaBArF4 was also found to cocatalyze, with (Phebox)Ir(OAc)(H), the acceptorless dehydrogenation of n-dodecane.

Synthesis of high surface area γ-Al2O3 as an efficient catalyst support for dehydrogenation of n-dodecane

In this work mesoporous nanocrystalline γ-Al2O3 has been synthesized by a three step (hydrolysis, condensation and hydrothermal treatment) sol–gel procedure in nitric acid medium with cationic surfactant (hexadecyltrimethyl ammonium bromide) as template. The prepared sample was employed as a carrier for the n-dodecane dehydrogenation catalyst. The synthesized samples were characterized by X-ray diffraction (XRD), N2 adsorption (BET), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric (TG) and temperature programmed reduction (TPR) techniques. The nitrogen adsorption analysis showed that the samples possessed mesoporous structure with high specific surface areas larger than 370 m2 g−1 and pore volumes larger than 1.5 cm3 g−1. The prepared samples also showed a high thermal stability up to 750 °C which is important for carrier of heterogeneous catalysts. The results of catalyst testing in the dehydrogenation reaction of n-dodecane confirmed that the synthesized support has a good potential to function as a carrier for n-dodecane dehydrogenation catalysts.

Enhancement of catalytic activity in dehydrogenation ofn-dodecane over nano-structured Pt-Sn/SBA-16 catalysts by microwave drying

In the present investigation, experimental results from a study of cubic SBA-16-supported Pt-Sn bimetallic catalysts used to investigate dehydrogenation ofn-dodecane to 1-dodecene are presented. Pt (1 wt%)-Sn (1 wt%)/SBA-16 catalyst is synthesized using a simple co-impregnation (CI) method. Further, the impregnated catalysts are dried separately using microwave drying (MW-D) and conventional electrical drying (CE-D) techniques. The microwave-mediated drying of Pt (1%)-Sn (1%)/SBA-16 shows a better catalytic performance and time-on-stream activity for the target reaction.

Fabrication of Nanodispersed Pt–Sn/SBA-16 Catalysts and Their Catalytic Applications

Abstract Monodispersed bimetallic Pt–Sn/SBA-16 catalysts prepared by coimpregnation technique and microwave-drying method showed enhanced catalytic activities for selective dehydrogenation of n-dodecane to its corresponding mono-olefins and preferential oxidation (PROX) of CO in the presence of excess H2.

Method for Metal Dispersion Measurements in Bimetallic Pt-Sn/Al2O3 Catalysts

A method for metal dispersion measurement in bimetallic Pt-Sn/Al2O3 catalysts using a combination of nonactivated and activated H2/O2 chemisorptive titrations has been attempted. Fractions of dispersed, unalloyed Pt, Pt(U), alloyed Pt, Pt(A) and alloyed Sn, Sn(A) may be determined by this method. The Pt(A) and Sn(A) contents of the catalysts correspond to a mole ratio (Pt/Sn) ≍ 1, (for catalysts containing 0.4 wt% Pt and Sn content ranging such that the atomic ratio of Sn to Pt varies from 0.25-8, in steps) indicating possible formation of an alloy phase, PtSn (1:1 mole basis). Turnover numbers for dehydrogenation of n-dodecane indicate that Sn increases overall dispersion of Pt by dilution/ensemble effects. Increasing the Sn:Pt ratio to 16 results in decreased dispersion. Typical trends in H2/O2 uptakes with respect to titration cycles for bimetallic Pt-Sn catalysts vis a vis monometallic Pt/Al2O3 catalysts are discussed.

IR-spectral study of the metal state in low-percentage alumina-rhenium and alumina-technethillm catalysts following high-temperature reductive treatment

The state of Re and Tc in low-percentage alumina-rhenium (0.25 % Re) and aluminatechnetium (0.1 % Tc) catalysts reduced by H2 at 500–900 °C was studied using IR spectra of the diffuse reflection of the adsorbed CO. A highly dispersed (probably two-dimensional) metal phase with a lowered electron-donating ability due to strong metal—support interaction is present on the surface of these catalysts along with the ionic forms of Re and Tc at +1 and +4 oxidation states. CO adsorbed on such metals in a linear form can be removed by evacuation even at ∼20°C. The amount of highly dispersed metal phase on the support surface increases monotonically with an increase in the activation temperature of Re/Al2O3 and Tc/Al2O3. The activity of the catalysts in the dehydrogenation ofn-dodecane varies directly with the concentration of the electron-deficient highly dispersed metal phase. It is therefore concluded that highly dispersed Re0 and Tc0 formed during high-temperature treatment by H2 are the precursors of the catalytically active centers in the paraffin dehydrogenation reaction.

Activation of low-percentage Re-Al2O3 and Tc-Al2O3 catalysts for the dehydrogenation of paraffins

The activity and selectivity of low-percentage (0.1–1 mass. %) Re-Al2O3 and Tc-Al2O3 catalysts in the dehydrogenation ofn-dodecane is shown to increase in response to an increase in the temperature of their activation in hydrogen from 500°C to 900°C. The activities of such catalysts are comparable to those of analogous alumina-platinum systems, while the selectivity of the former catalysts inn-monoolefin production is higher than that of the latter.

Synthesis of alkylsalicylate additives based on dodecylphenols

Because the resources of solid paraffins used in producing the additive MASK are limited, the search for sources of olefinic raw material for the production of alkylsalicylate additives is an urgent task. In Czechoslovakia, a process has been developed for obtaining linear olefins by dehydrogenation of n-dodecane. On the basis of this process, alkylsalicylate additives have been synthesized, and tested, and their properties compared with MASK. The properties of the samples for the most part satisfy the requirements for MASK additives. These studies show that it is possible in principle to synthesize effective alkylsalicylate additives for lube oils on the basis of linear olefins obtained by dehydrogenation of n-dodecane.

Oxidative dehydrogenation of n-dodecane: G. V. Isagulyants, O. D. Sterligov, S. V. Abel'son and L. V. Fed'ko, Neftekhimiya 23, No. 3, 331–334, 1983

Oxidative dehydrogenation of n-dodecane: G. V. Isagulyants, O. D. Sterligov, S. V. Abel'son and L. V. Fed'ko, Neftekhimiya 23, No. 3, 331–334, 1983

Effect of the platinum concentration in alumina-platinum catalysts in the dehydrogenation of higher linear paraffins

1. The effect of the platinum concentration in the range from 0.05 to 1.0% on platinum particle size was studied in the case of alumina-platinum catalysts containing 1% lithium and not containing lithium. The dehydrogenation of n-dodecane at 480‡C under hydrogen pressure was also studied. 2. Platinum particle size increases with increasing platinum concentration in all the catalysts. 3. The catalyst selectivity relative to monoolefin formation at different conversions is independent of the platinum concentration and depends only on the addition of lithium. 4. Catalysts containing from 0.25 to 1.0% platinum have the same specific activity in the dehydrogenation of n-dodecane. The specific activity of catalysts with 0.05% Pt is higher than for catalysts with higher platinum contents, independently of the method of preparation and addition of lithium.

Effect of included oxygen and water vapor on the dehydrogenation of n-dodecane on an aluminum-chromium-potassium catalyst

1. The presence of ∼300–1000 ppm of oxygen and water in the hydrogen feed has a negative effect on the activity and selectivity of those aluminum-chromium-potassium catalysts which are used in the dehydrogenation of n-dodecane under hydrogen pressure. 2. Rapid elimination of included O2 with the formation of H2O occurs during catalytic hydrocarbon dehydrogenation. The fraction of active centers involved in this elimination process is small, and the formation of H2O has essentially no effect on the dehydrogenation rate. 3. The poisoning of the aluminum-chromium-potassium catalyst by O2 is in reality a matter of poisoning by water.

Effect of sulphur compounds on dehydrogenation of n-dodecane in the presence of an alumina-chromium-potassium catalyst

1. 1. A study was made of the effect of elementary sulphur, hydrogen sulphide, thiophen and diethyldisulphide additives (sulphur concentration 0·0006–0·01%) on dehydrogenation of n-dodecane containing 0·0005% total sulphur, in the presence of an alumina-chromium-potassium catalysts (500°C; 0·4 MPa, space velocity 40 hr −1, molar dilution with hydrogen 8) in experiments taking up to 6 hr. 2. 2. It was shown that thiophen already in a concentration of 0·0006% S and elementary sulphur, hydrogen sulphide and diethyldisulphide in a concentration of 0·007–0·01% S have a toxic effect on the catalyst, reducing its activity and selectivity, the toxic effect depending on the type of sulphur compound. Catalyst activity may be restored by oxidizing regeneration.

Determination of the boiling points of straight-chain C 12- alkenes from their gas chromatographic retention indices

The boiling points of all the eleven straight-chain dodecenes were calculated from the retention indices measured for the individual n-dodecenes. These indices were determined directly from a technical mixture of n-dodecenes obtained by the catalytic dehydrogenation of n-dodecane. A method based on the constants of the proportionality between boiling points and retention indices, as well as the dependence of the above constants on the number of carbon atoms, on the structure of the isomers under comparison, and on the column temperature, was employed for the calculation. The reproducibility of the boiling points calculated from different references isomers or column temperatures was within ± 0.1°. The calculated boiling points of the n-dodecenes were compared with those from a method of calculation depending on the boiling points of n-alkanes between which the n-alkene is eluted (maximum deviation −1.9 °) as well as from a calculation according to the corrected index boiling points (maximum deviation −0.4 °).