Dehydrogenation Research Articles

THE DESORPTION AND DISSOCIATION OF ETHYLENE (C2H4) ON Ru(1 010) SURFACE

The ethylene (C2H4) adsorbed on Ru(1010) surface has been studied by X-ray photoelectron spectroscopy (XPS),thermal desorption spectroscop y (TDS) and ultraviolet photoelectron spectroscopy (UPS).The results show that e thylene absorbs in molecular state on Ru(1010) surface stably below 200K.The deh ydrogenation of ethylene occurs at 200K.The main product of the dehydrogenation of the absorbed ethylene is the acetylene (C2H2). After th e dehydrogenation of the absorbed ethylene,the C1s shifts 0.3eV to low binding e nergy level,and the binding energies of σCC and σCH bond have an increase of 0.5eV and 1.1eV respectively.

Catalytic dehydrogenation (DH) of light paraffins combined with selective hydrogen combustion (SHC): II. DH+SHC catalysts physically mixed (redox process mode)

When a physical mixture composed of a 0.7 wt.% Pt–Sn-ZSM-5 dehydrogenation (DH) catalyst and a 42 wt.% Bi 2O 3/SiO 2 selective hydrogen combustion (SHC) catalyst is subjected to a DH + SHC redox process operation, it gives substantially higher than equilibrium propylene yields from propane. At 540°C, atmospheric pressure and WHSV of 2 h −1, initial microreactor propylene yields from neat propane are 48.2% at about 90% selectivity, compared to equilibrium olefin yields of 20.0% at about 95% selectivity when only the DH catalyst is used. The overall propylene yield improvement is 140%. In this novel redox process arrangement no gaseous oxygen is cofed to the physical mixture; the lattice oxygen of the SHC catalyst is the sole oxidizing agent to selectively combust the hydrogen produced in situ by the dehydrogenation of the propane, catalyzed by the commingled DH catalyst. Periodic regeneration with air is necessary to replenish the lattice oxygen of the SHC catalyst depleted in the redox reaction. Although still significantly (i.e., 65%) above equlibrium, the high initial DH + SHC propylene yields are not sustainable and decline from 48.2% (first cycle) to 33.0% (tenth cycle); i.e., 2.1%/cycle; they are ascribed to the loss of Bi 2O 3 dispersion on the SiO 2 support caused by the deep redox cycling. Shortening the redox cycle or increasing the SHC/DH catalyst ratio lessen the decline. However, the identification of a more redox stable catalyst is imperative to make the process practical. Some suggestions are provided. It is surmised that the DH + SHC redox process approach will ultimately (i.e., once a sufficiently redox stable SHC catalyst is identified) be preferred over the DH- > SHC- > DH cofed approach to improve conventional dehydrogenation processes such as the Oleflex and Catofin processes.

Catalytic dehydrogenation (DH) of light paraffins combined with selective hydrogen combustion (SHC): I. DH → SHC → DH catalysts in series (co-fed process mode)

Sb 2O 4, In 2O 3, WO 3 and Bi 2O 3, supported on 50% SiO 2, were found to be highly selective hydrogen combustion (SHC) catalysts. Their respective selectivities are 99.8, 99.7, 98.5 and 98.1% at 500°C, atm pressure, WHSV 2 h −1 and C ° 3/C 3 =/H 2/O 2 = 80/20/20/10. Their activities vary greatly, reflected by the first-order hydrogen combustion constants ( k H 2 , s −1) which are: In 2O 3 1.57, Bi 2O 3 0.53, WO 3 0.36, Sb 2O 4 0.22. Among the SiO 2, Al 2O 3, TiO 2 and ZrO 2 supports tested, ZrO 2 was found to be the best overall carrier for the highly active In 2O 3. When a 0.7 wt% Pt-Sn-ZSM-5 dehydrogenation (DH) catalyst and a 10 wt% In 2O 3/ZrO 2 SHC catalyst are used in a sequential microreactor DH → SHC → DH co-fed process mode, higher than equilibrium yields of light olefins are obtained from the corresponding paraffins. At 550°C, atmospheric pressure and WHSV of 2 h −1 propylene yields of 29.7% at 97% selectivity (0.3 air/propane in SHC), and 33% at 89% selectivity (0.6 air/propane in SHC) are realized, compared to the equilibrium yield of 25% at 99% selectivity when only the DH catalyst is used. The yield improvements over equilibrium dehydrogenation are 19 and 32%, respectively. Under the same operating conditions but 0.2 air/isobutane ratio in the SHC stage, the isobutylene yield from isobutane is 47.5% at 99+% selectivity as compared to 40% and 99+% selectivity when only the DH catalyst is used; i.e. an 18% yield improvement over equilibrium. The above metal oxide SHC catalyst systems might find application to improve conventional DH processes such as Oleflex and Catofin.

Changes in surface and catalytic dehydration activities of 2-propanol on AlPO-5 induced by silver impregnation

Five samples of pure Al-Phosphates (ALPO-5) and silver oxide impregnated Al-Phosphates (wt.% of Ag=1.5–8.0) were prepared. The structural characterization was studied using X-ray diffraction (XRD) and FT-IR techniques. The textural properties (surface area end mean pore radius) were determined from N 2 adsorption at 77 K. Surface acidities of all prepared samples was estimated by nonaqueous titration of solid catalysts with n-butylamine using Hammett’s indicators. The catalytic conversion of 2-propanol at 300°C was also performed using microcatalytic pulse technique. Both XRD and FT-IR techniques give the characteristic ALPO-5 patterns only, whereas Ag 2O-AlPO-5 or silver-aluminium phosphate spinel were not be detected. The surface area, mean pore radius, surface acidity and catalytic activity were overall increased upon increasing the loading amounts of silver. Pure and silver impregnated aluminium phosphates show no dehydrogenation (DHG) activity. Impregnation with silver favors dehydration of 2-propanol to ether via intermolecular reaction which can proceed on weak acid sites.

Two moles of O2 consumption and one mole of H2O2 formation during cholesterol peroxidation with cholesterol oxidase from Pseudomonas sp. strain ST-200.

Cholesterol oxidase from Pseudomonas sp. strain ST-200 oxidized cholesterol and cholestanol to 6beta-hydroperoxycholest-4-en-3-one and 5alpha-cholestan-3-one respectively. The former was converted spontaneously to several oxysteroids such as 6-hydroxycholest-4-en-3-one and cholest-4-ene-3,6-dione, with the consumption of 2 mol of O(2) and the formation of 1 mol of H(2)O(2) for each mole of cholesterol oxidized. An oxidized form of the cholesterol oxidase dehydrogenates cholesterol, probably to the 5-en-3-one derivative. A reduced form of the enzyme, yielded from the cholesterol dehydrogenation reaction, dioxygenated cholest-5-en-3-one to 6beta-hydroperoxycholest-4-en-3-one.

Metal Oxides As Selective Hydrogen Combustion (SHC) Catalysts and Their Potential in Light Paraffin Dehydrogenation

An alternative approach to light paraffin dehydrogenation (thermodynamically limited) and oxydehydrogenation (thermodynamically not limited) is a combination process of dehydrogenation (DH) with selective hydrogen combustion (SHC). By selectively combusting the hydrogen produced in the DH reaction, the overall combination process becomes thermodynamically not limited. While dehydrogenation is commercially practiced, the olefin yields are equilibrium limited, and the process is endothermic, requiring large inputs of external heat, and cyclic, requiring frequent catalyst regenerations. Oxydehydrogenation, while not equilibrium limited, suffers from low selectivity at high conversions with currently known catalysts and is therefore not practiced commercially.For these reasons we have launched a study of DH-SHC. The first task is the discovery and identification of good SHC catalysts, which are reported here. We have discovered that certain metal oxides oxidize hydrogen with great preference to propane and propylene, making them good candidates for an eventual DH-SHC process. Among the best are Bi2O3(>99% sel.), Bi2Mo3O12(99% sel.), and In2Mo3O12(98.4% sel.). In stark contrast to these compositions stands V2O5, which attacks hydrocarbons with great preference to hydrogen, resulting in a hydrogen oxidation selectivity of only 6.1%. It is noteworthy that all of the good SHC catalysts contain elements which have a lone pair of electrons in their prevailing oxidation state at the start of the reaction (redox mode) or under steady-state operating conditions (cofed mode).The experiments were carried out at atmospheric pressure and in the range of 500°C with gravimetric methods using a Cahn balance, and redox and cofed methods using an automated microreactor.The best SHC compositions identified in this study constitute promising candidates for a proposed DH-SHC process and their viability in this context is reported in a separate study (1).

BUFFERING OF INCOMPATIBLE ELEMENTS IN THE LITHOSPHERIC MANTLE DURING MELT PERCOLATION: THE ROLE OF HYDROUS PHASES

An increasing number of highly precise and accurate whole-rock trace element data is becoming available for orogenic peridotites and mantle xenoliths. Extreme LILE enrichment relative to HFSE is a common feature which is generally attributed to pervasive forms of metasomatism modelled in terms of chromatographic crystallisation effects (Navon and Stolper, 1987), possibly coupled with sink/source effects (Godard et al., 1995). Models describing propagation of melt batches through mantle rocks (Godard et al., 1995; Vernieres et al., 1997) usually provide satisfactory numerical simulations for the observed LILE variations, and particularly for LREE enrichment in interstitial melts and minerals. However, they often do not account for the wide range of variations of HFSE and U, Th. Uranium anomalies may result from selective transport by fluids (Alard et al., 1999), whereas inconsistencies between measured and predicted HFSE abundances are frequently ascribed to buffering exerted by elusive Ti-oxides (Bodinier et al., 1996), particularly rutile, which is claimed to produce intra-HFSE fractionation (i.e., Zr, Hf and Ta, Nb decoupling). However, rutile is not commonly found in mantle assemblages, and experiments have shown that an unusually TiO2-rich bulk rock composition is required to stabilize rutile (Ayers et al., 1997). The hydrous phases phlogopite, pargasite/kaersutite and richterite could play a significant role in buffering LILE in the lithospheric mantle and must be also considered as either a complement or an alternative to Ti-oxides in buffering HFSE. Phlogopite is stable up to 1200°C at pressures higher than 20 kbar (Mengel and Green, 1989), whereas pargasite and kaersutite are stable up to 1150°C in the 25-30 kbar range under water-undersaturated conditions (Niida and Green, 1999). Phlogopite and amphibole are expected to form during migration of alkaline melts through the upper mantle domain, thus resulting in sink/source effects and buffering of incompatible elements. The buffering role of phlogopite can be easily predicted: Schmidt et al. (1999) showed that DRb is significantly higher than 1, whereas DSr is in the range 0.02-0.06, thus causing a strong decrease of Rb/Sr in the interstitial melt. Interestingly, DTi and DBa may approach or even exceed unity (DBa up to 1.6), confirming their dependence on the Ti-oxy-substitution that is expected to increase the phlogopite stability. Therefore, a more effective coupled buffering of Ba and Ti is expected at increasingly lower XH2O conditions. Among the other elements, only Nb, Li and Zr may be retained to some extent (Ds are 0.07, 0.02 and 0.015, respectively). Although very low, DPb (0.02) is at least two orders of magnitude greater than DU,Th, which are in the order 10-4-10-6, like those of the REE. Amphibole shows more complex behaviour. From an integrated experimental, analytical and crystallographic approach we can show that trace-element partitioning behaviour differs significantly between pargasite/kaersutite and richterite. Moreover, it cannot be predicted without taking into account both the presence of dehydrogenation and the complete site distribution of the major elements. In K-richterites, Ds >1, permitting effective buffering by amphibole, are observed only for Sr, F, V, Cr; whereas Ds for the other elements are 1 and a decoupling of HFSE is observed. The Amph/LiqDNb/Ta is highly variable (0.7-1.7), and is ruled by the dimensions of the M1 site, which in turn depends on its Fe, Mg and Ti content. Surprisingly, pargasite/kaersutite has higher partition coefficients and consequently a stronger buffering capacity for Rb, Ba and Cs than K-richterite. This is not the case for Sr, which has a higher compatibility in Krichterite, which provides larger and less constrained M4 sites. New partitioning data reveal that the buffering of incompatible elements by hydrous phases can be modelled with confidence only if appropriate assumptions about phase stability (and hence the geodynamic environment) and composition are made. The prediction of the behaviour of HFSE requires a reasonable estimate of the water and titanium activity in the melt. Ds of elements which are involved in charge compensation of the oxy-component (Ba and Ti in phlogopite and Ti, Nb and Ta in amphiboles) cannot be assumed to be constant during the precipitation of hydrous phases from the interstitial melt. Phlogopite with no oxy- or F- components has about 4 wt% H2O, whereas a similar pargasite/ richterite has about 2.0 wt% H2O. Former crystallisation of hydrous phases implies sink/source effects for both H and Ti, which in turn either affect D in hydrous phases crystallised later or prevent the formation of new hydrous phase beyond the reaction zone.

From New Zirconium-Phosphanide to Phosphinidene Complexes

Lithiated primary silylphosphanes and -arsanes react with rircOnocene-chloride-hydride to give planar Zr(III)2-E2-ringsystems (R = SiMc2Thex (I), Si(i-Pr)3, SiF(t-Bu)Is). However, the complexes can also be synthesized by conversion of zirconocene-dichloride with lithiated silylphosphanes. Reductive dehydrogenation of 1 through heating with Pd on activated charcoal or [(Ph3P)2Pt(C2H4)] in toluene leads to 2.

Studies of the roles of Sn or Fe on γ-Al 2 O 3 -supported Pt catalysts by CO adsorption microcalorimetry and dehydrogenation reaction of C 4 alkanes

CO adsorption microcalorimetry was employed in the study of γ-Al2O3-supported Pt, Pt-Sn and Pt-Fe catalysts. The results indicated that the initial differential heat of CO adsorption of the Pt/γ-Al2O3 catalyst was 125 kJ/mol. As CO coverage increased, the differential heat of adsorption decreased. At higher coverages, the differential heat of adsorption decreased significantly. 60% of the differential heat of CO adsorption on the Pt/γ-N2O3 catalyst was higher than 100 kJ/mol. No significant effect on the initial differential heat was found after adding Sn and Fe to the Pt/γ-Al2O3 catalyst. The amount of strong CO adsorption sites decreased, while the portion of CO adsorption sites with differential heat of 60–110 kJ/mol increased after increasing the Sn or Fe content. This indicates that the surface adsorption energy was changed by adding Sn or Fe to Pt/γ-N2O3. The distribution of differential heat of CO adsorption on the Pt-Sn(C)/γ-Al2O3 catalyst was broad and homogeneous. Comparison of the dehydrogenation performance of C4 alkanes with the number of CO adsorption sites with differential heat of 60–110 kJ/mol showed a good correlation. These results indicate that the surface Pt centers with differential heats of 60–110 kJ/mol for CO adsorption possess superior activity for the dehydrogenation of alkanes.

Textural, Structural and Catalytic Properties of ZnCr2O4–A12O3 Ternary Solid Catalysts

Two series of ternary solid catalysts containing Al, Cr and Zn but with different ZN2+ or Cr3+ ion contents were prepared by impregnation methods. All systems were calcined by heating within the temperature range 773–1073 K. Structural characterization of the systems was effected by X-ray diffraction (XRD) methods and by differential thermal analysis (DTA). The textural properties of the precalcined products were measured from adsorption/desorption studies of nitrogen at 77 K. The surface acidities of the precalcined products were also studied using a poisoning method employing pyridine as the probe base. The adsorption and disproportionation of NO at 298 K was followed via in-situ FT-IR spectroscopic methods, while the catalytic activities of the prepared samples towards the dehydration (DHD)/dehydrogenation (DHG) of propan-2-ol were studied using a pulse microcatalytic technique. XRD and DTA analyses showed the presence of γ-A12O3 and ZnCr2O4 in the prepared samples but did not provide any evidence for other detectable species in the ternary solid materials. The disproportionation of NO, as well as the catalytic conversion of propan-2-ol, was apparently strongly influenced by the structural properties of these materials but to a lesser extent by their textural properties.

97/00172 Analysis and dehydrogenation of coal liquefied oils

97/00172 Analysis and dehydrogenation of coal liquefied oils

Generation of Thiazoles by Column Dehydrogenation of Thiazolidines with MnO2

Generation of Thiazoles by Column Dehydrogenation of Thiazolidines with MnO2

Dispironaphthalenones and spironaphthalenones as novel dehydrogenation reagents

Dehydrogenation of a number of dihydroaromatic substrates has been carried out using either dispironaphthalenone 1 or spironaphthalenones 2 & 3 as dehydrogenating agents. The reaction is over in refluxing mesitylene in 1– hr and the yields of the aromatised products are fairly good (65–70%).

Decomposition of isopropanol on magnesium oxide/silica in relation to texture, acidity and chemical composition

Two series of MgO/SiO 2 catalysts were prepared either by mechanical mixing (MM) or by co-precipitation (COP) in the composition range 16–83 mol-%. Catalysts calcined at 500, 600 and 800°C were characterised by nitrogen adsorption, chemisorption of pyridine at 150°C, and catalytic conversion of 2-propanol at 260°C. Dehydration (DHD) and dehydrogenation (DHG) were independent of available S BET, although DHG was much favoured by low-area catalysts. DHD to propene dropped by pre-treatment at 800°C due to the formation of enstatite and to the decrease in surface hydroxyls involved in catalysis. DHD and total conversion of alcohol increased linearly as a function of surface acidity per unit area, whereas DHG exhibited a reverse behaviour. In general, COP catalysts catalyze decomposition to a higher degree in comparison to the corresponding MM catalysts.

Darstellung von Benzo[c]thiophenen nach neueren Varianten der Hinsberg‐Reaktion

Preparation of Benzo[c]thiophenes Using a Modified Hinsberg‐ReactionWhereas the tetrahydrobenzo[c]thiophenes 3 and 6 are easily obtained from 1 and 2 or 4 their dehydrogenation (i. e. aromatization) is difficult and the yields are low. However, the method allows to prepare hitherto unknown benzo[c]thiophenes with special substituents in the 1,3‐positions.

Highly effective dehydrogenation of steroid isoxazolines

Highly effective dehydrogenation of steroid isoxazolines

Eraction Ergodography for Dehydrogenation of Silathione

Eraction Ergodography for Dehydrogenation of Silathione

Photosensitized Dehydrogenation of Flavanones to Flavones Using 2,4,6-Triphenylpyrylium Tetrafluoroborate (TPT)

Photosensitized Dehydrogenation of Flavanones to Flavones Using 2,4,6-Triphenylpyrylium Tetrafluoroborate (TPT)

ChemInform Abstract: Activity of Dehydrogenating Catalysts.

ChemInformVolume 19, Issue 43 Preparative Organic Chemistry ChemInform Abstract: Activity of Dehydrogenating Catalysts. G. GARDOS, G. GARDOS Vesz. Veg. Egyetem, Asvan. Szentechnol. Intezet, Veszprem, HungarySearch for more papers by this authorI. MEZO, I. MEZO Vesz. Veg. Egyetem, Asvan. Szentechnol. Intezet, Veszprem, HungarySearch for more papers by this author G. GARDOS, G. GARDOS Vesz. Veg. Egyetem, Asvan. Szentechnol. Intezet, Veszprem, HungarySearch for more papers by this authorI. MEZO, I. MEZO Vesz. Veg. Egyetem, Asvan. Szentechnol. Intezet, Veszprem, HungarySearch for more papers by this author First published: October 25, 1988 https://doi.org/10.1002/chin.198843110AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume19, Issue43October 25, 1988 RelatedInformation

ChemInform Abstract: Carbinolamine as Precursors of Lactams in Mercuric Dehydrogenations.

AbstractDie Dehydrierung des Trimethylpiperidins (I) mit Hg(II)‐Verbindungen liefert das Piperidon (II) und das Dehydropiperidin (III).