Reaction Of Propane Research Articles

Selective Introduction of Acid Sites in Different Confined Positions in ZSM-5 and Its Catalytic Implications

Controlling the location of acid sites in zeolites can have a great effect on catalysis. In this work we face the objective of directing the location of Al into the 10R channels of ZSM-5 by taking advantage of the structural preference of B to occupy certain positions at the channel intersections, as suggested by theoretical calculations. The synthesis of B-Al-ZSM-5 zeolites with variable Si/Al and Si/B ratios, followed by B removal in a postsynthesis treatment, produces ZSM-5 samples enriched in Al occupying positions at 10R channels. The location of the acid sites is determined on the basis of the product distribution of 1-hexene cracking as a test reaction. The higher selectivity to propene and lower C4=/C3= ratio in the samples synthesized with B and subsequently deboronated can be related to a larger concentration of acid sites in 10R channels, where monomolecular cracking occurs. Finally, several ZSM-5 samples have been tested in the methanol to propene reaction, and those synthesized through the B-...

The Role of External Acidity of Hierarchical ZSM‐5 Zeolites in n‐Heptane Catalytic Cracking

AbstractThe hierarchical ZSM‐5 zeolite, which contains mesopores in addition to intrinsic micropores, is expected to enhance the bulky molecular diffusion and accessibility of acid sites. These sites, distributed in the internal surface (micropore) or external environment (including external surface and mesopore walls), play different roles in chemical reactions. To explore the effect of internal/external acidity on the reaction, in this study, a series of hierarchical ZSM‐5 zeolites with similar pore structures but different external acid properties were synthesized. Tartaric acid was employed to poison the acidic sites in the external environment selectively and extract Al from the framework. The catalytic cracking of n‐heptane (the main compound of naphtha) was chosen as a model reaction. The results show that elimination of external active sites tends to reduce the coke formation. The more external acid sites are selectively eliminated, the better catalytic performance can be achieved because of suppressing the bimolecular reactions of ethylene and propylene.

Insights into the role of silanols in methanol to propene reaction over silicalite-2 zeolite through post-treatments

As an efficient catalyst in methanol to propene (MTP), silicalite-2 zeolite was subjected to acidization and desilication. Changes in the properties of modified zeolites were investigated by XRD, FTIR, SEM, TPD, and sorption techniques. It was shown that the samples through post-treatments all showed a similar initial catalytic activity, while the deactivation behaviors were distinct. Samples through desilication exhibited a 2-fold improvement in catalytic lifetime (methanol conversion falling to 95%), while acidization accelerated the deactivation apparently. The results from in-situ FTIR and OH-FTIR revealed that the accessibility of acid sites (mainly H-bonded silanols) determines the initial activity and the location of isolated silanols is crucial for deactivation. The isolated silanols in the pore can impact the formation and diffusion of the intermediate species and subsequently affects the coke capacity and mobility. The external surface is indicated to be responsible for the tolerance of external coke. Thus, less internal isolated silanols and larger external surface area can jointly contribute to a long catalytic lifetime over silicalite zeolite.

Effect of CO2 in the oxidative dehydrogenation reaction of propane over Cr/ZrO2 catalysts

Investigation was made on the effect of chromium content, and method of hydrothermal preparation of Cr/ZrO2 catalysts on their catalytic properties for CO2 oxidative dehydrogenation of propane (ODP). The catalysts were characterized by nitrogen physisorption, X-ray diffraction, Raman spectroscopy, and temperature programmed reduction and desorption of CO2 (TPD-CO2). The Cr/ZrO2 catalysts containing various chromium contents between 2.5 and 15 wt.% of Cr were prepared by conventional and microwave-assisted hydrothermal methods. Tetragonal ZrO2 was formed, with higher Cr contents, and smaller crystallite sizes obtained using the microwave-assisted method. The relationship between selectivity to propene and propane conversion suggested that independent of the preparation method, the catalytic properties could be classified in two groups, with low and high chromium contents. The TPD-CO2 results showed that a fraction of the CO2 was desorbed at temperatures higher than 500 °C, with simultaneous reduction of Cr(VI) species. The presence of CO2 in the reactants caused strong decreases of activity, selectivity, and yield towards propene. These results suggested that CO2 adsorbed strongly on the chromium oxide active sites for dehydrogenation of propane. The Cr/ZrO2 catalysts were active and selective for dehydrogenation of propane in the absence of CO2 (CDP), and became deactivated with time on stream. The activity was reestablished by thermal treatment with CO2 or O2 after deactivation in CDP catalytic cycles, with the activity always being reestablished by treatment in O2. The deactivation occurred by reduction of Cr(VI) species and by deposition of carbonaceous species produced in oligomerization reactions.

RuxCe1-xO2-y nanoparticles deposited on functionalized γ-Al2O3 as a thermally stable oxidation catalyst

Structural stability of ceria in catalysts used for reactions occurring at elevated temperatures is an important technological problem. In this work, we propose a simple method that should improve the thermal stability of Ru doped ceria nanoparticles supported on alumina.Nanosized (≤5 nm), ruthenium doped ceria particles were synthesized by the reverse microemulsion method and then deposited on the functionalized γ-Al2O3 support. Obtained catalysts were investigated using a wide range of characterization methods (e.g. XRD, HRTEM, STEM-HAADF, H2-TPR, XPS) to determine the dispersion and stability of ceria in the oxidizing and reducing atmosphere. The catalytic activity of the samples was tested in the reaction of soot and propane combustion.It has been shown that covering of γ-Al2O3 support with a monolayer of decanoic acid enabled uniform dispersion of RuxCe1-xO2-y nanoparticles and their very high resistance against sintering up to 800 °C in the oxidizing and especially in the reducing atmosphere. The ceria particles show also high reducibility at the low-temperature range (˂500 °C), what positively influences on their catalytic activity in the oxidation processes. Ru0.05Ce0.95O2-y deposited on the functionalized alumina is an active and stable catalyst for total oxidation of soot (T50 = 487 °C) and propane (T50 = 225 °C).

Reaction of propane with the ordered NiO/Rh(1 1 1) studied by XPS and LEISS

Nickel oxide has been reported to be an efficient catalyst for oxidative dehydrogenation of propane (ODP) to propene at low temperature. In this paper, ultrathin NiO films with various thickness were prepared on a Rh(1 1 1) surface and characterized by X-ray photoemission spectroscopy (XPS) and Low-energy ion scattering spectroscopy (LEISS). Results show that NiO forms a two-dimensional (2D) network with a O-Ni-O structure at submonolayer coverages, and a bulk-like NiO at multilayer coverages. The submonolayer NiO films are less stable than the thick ones when annealed in ultra-high vacuum (UHV) due to the strong interaction with the Rh substrate. Propane was dosed onto the model surfaces at different temperatures to investigate the activation of propane and reactivity of NiO films with propane. The reactions of propane with the thin and thick NiO films are significantly different. Propane activates on the O defect sites for the thick NiO films, whereas activation occurs on the interface of nickel oxide and substrate for the thin films with a higher activity.

Synthesis of high-Si hierarchical beta zeolites without mesoporogen and their catalytic application in the methanol to propene reaction

High-Si single-crystalline beta zeolites with intracrystal mesopores were synthesized for the first time and investigated as catalysts for the methanol to propene (MTP) reaction.

In Situ Assembly of Nanoparticles into Hierarchical Beta Zeolite with Tailored Simple Organic Molecule.

A hierarchically structured beta zeolite with intercrystalline mesopores was successfully synthesized via in situ assembly of nanoparticles by employing a simple organic molecule N2-p-N2, tailored from polyquaternium surfactant, with no hydrophobic long chain. The generated samples were studied by using powder X-ray diffraction (XRD) and nitrogen adsorption/desorption isotherms. Computer simulation, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) technologies were also used. The characterized results show that the tailored template molecule N2-p-N2 without hydrophobic long-chain tail still can direct the zeolite crystallization, while the hydrophobic long-chain tail is not necessary during the mesoporous Beta zeolite formation. The catalytic performances of the sample were studied using alkylation of benzene with propene reaction to evaluate the relationship between the structure and property. The results apparently suggested an overall improved resistance against deactivation as compared to conventional beta zeolite in reactions. Furthermore, this tailored simple organic molecule strategy from dual-functional surfactant for making mesoporous zeolite would offer a new method of synthesizing other hierarchically structured zeolites.

Reaction Sensitivity of Ceria Morphology Effect on Ni/CeO2 Catalysis in Propane Oxidation Reactions.

CeO2 nanocubes (c-CeO2), nanoparticles (p-CeO2), and nanorods calcined at 500 °C (r-CeO2-500) and 700 °C (r-CeO2-700) were used as supports to synthesize a series of Ni/CeO2 catalysts for the propane combustion and oxidative dehydrogenation of propane (ODHP) reactions. The Ni-CeO2 interaction greatly promotes the reducibility of CeO2, but CeO2 morphology-dependent Ni-CeO2 interaction was observed to form different speciation of Ni species (Ni2+ dissolved in CeO2, highly dispersive NiO, NiO aggregate) and oxygen species (strongly activated oxygen species, medially activated oxygen species, weakly activated oxygen species) in various Ni/CeO2 catalysts. Ni-CeO2 interaction is stronger in Ni/c-CeO2 catalysts than in other Ni/CeO2 catalysts. Different morphology-dependences of Ni/CeO2 catalysts in propane combustion and ODHP reactions were observed. The Ni/r-CeO2-500 catalyst with the largest strongly activated oxygen species is most catalytic active in the propane combustion reaction while the Ni/c-CeO2 catalyst with the largest amount of weakly activated oxygen species exhibits the best catalytic performance in the ODHP reaction. Thus, the CeO2 morphology engineering strategy is effective in finely tuning the metal-CeO2 interaction and the reactivity of oxygen species to meet the requirements of different types of catalytic oxidation reactions.

The levels, variation characteristics, and sources of atmospheric non-methane hydrocarbon compounds during wintertime in Beijing, China

Abstract. Atmospheric non-methane hydrocarbon compounds (NMHCs) were measured at a sampling site in Beijing city from 15 December 2015 to 14 January 2016 to recognize their pollution levels, variation characteristics, and sources. We quantified 53 NMHCs, and the proportions of alkanes, alkenes, acetylene, and aromatics to the total NMHCs were 49.8–55.8, 21.5–24.7, 13.5–15.9, and 9.3–10.7 %, respectively. The variation trends in the NMHC concentrations were basically identical and exhibited remarkable fluctuation, which was mainly ascribed to the variation in meteorological conditions, especially wind speed. The diurnal variations in NMHCs on clear days exhibited two peaks during the morning and evening rush hours, whereas the rush hours' peaks diminished or even disappeared on the haze days, implying that the relative contribution of the vehicular emissions to atmospheric NMHCs depended on the pollution status. Two evident peaks of the propane ∕ propene ratios appeared in the early morning before sun rise and at noontime on clear days, whereas only one peak occurred in the afternoon during the haze days, which were attributed to the relatively fast reactions of propene with OH, NO3, and O3. Based on the chemical kinetic equations, the daytime OH concentrations were calculated to be in the range of 3. 47 × 105–1. 04 × 106 molecules cm−3 on clear days and 6. 42 × 105–2. 35 × 106 molecules cm−3 on haze days. The nighttime NO3 concentrations were calculated to be in the range of 2. 82 × 109–4. 86 × 109 molecules cm−3 on clear days. The correlation coefficients of typical hydrocarbon pairs (benzene ∕ toluene, o-xylene ∕ m,p-xylene, isopentane ∕ n-pentane, etc.) revealed that vehicular emissions and coal combustion were important sources for atmospheric NMHCs in Beijing during the wintertime. Five major emission sources for atmospheric NMHCs in Beijing during the wintertime were further identified by positive matrix factorization (PMF), including gasoline-related emissions (gasoline exhaust and evaporation), coal combustion, diesel exhaust, acetylene-related emissions, and consumer and household products. Coal combustion (probably domestic coal combustion) was found to make the greatest contribution (29.6–33.4 %) to atmospheric NMHCs during haze days.

Assessment of thermal explosion for an industrial recovery reactor by GC/MS product analysis combined with calorimetric techniques

The reaction of propylene with adsorbents such as BASF selexsorb CD and UOP of various sizes was studied. Adiabatic runaway tests were conducted on propylene mixed with various adsorbents to obtain knowledge on the thermal profile of each. Thermokinetic data were obtained from non-isothermal calorimetric study from the oligomerized reaction between propylene and various adsorbents. A detailed distribution of sorbent product from the adsorber has been analyzed for carbon product greater than 6 ( >C6) using gas chromatography/mass spectrometry results. The test revealed oligomerization and carbonaceous deposit formation of the adsorbent products. The reason for over-temperature of the reactor wall can be anticipated from the agglomeration of carbonaceous deposit disrupting the normal flow of propylene stream causing channeling and lowering the carry-away of heat-accumulated. This approach of real conditions, along with the simulation of process design and operation using computational fluid dynamics (CFD) studies, can render safer process information for avoiding the occurrence of similar runaway explosion induced industrial disaster.

Effect of the nature of the active-component precursor on the properties of Pt/MgAlO x catalysts in propane and n-decane dehydrogenation

The Pt/MgAlO x catalysts, in which a mixed aluminum–magnesium oxide obtained by the heat treatment of corresponding layered double hydroxides was used as a support, were studied. The effects of the nature of active-component precursors ([PtCl6]2–, [PtCl4]2–, and [Pt3(CO)6] 6 2- ), and the Mg/Al ratio in the support on the anchoring of complexes, the disperse state of platinum, and the properties of the obtained catalysts in the reactions of propane and n-decane dehydrogenation were found.

Reaction and deactivation of propylene over SAPO-34 at low temperature

We report the low temperature conversion of propylene with SAPO-34 zeolite as the catalyst, as a branched route in process of methanol to propylene (MTP). The maximum conversion of propylene occurred at 300°C, corresponding to the activation of propylene over low temperature acid sites of zeolite. With rate constant calculation and coke analysis at low temperature, we confirmed that adamantane is easily produced from propylene and it does not contribute to the increased conversion of reactants, but results in the cage blockage of zeolite. By detailed coke analysis and product distribution analysis, we proposed cyclic olefins, not aromatics, played the important role in hydrocarbon pool. In this regard, low temperature shows negative effect on MTP process considering the quick conversion of propylene to other olefins and the formation of adamantane, ignore of the increased ratio of propylene to ethylene ratio. The result provided new insight on the reaction mechanism of MTO/MTP system.

Adsorption and desorption of propane on Pd (111): A van der Waals density functional study. Energy binding sites and geometries

Palladium supported catalysts used for the partial oxidation of propane reaction aiming the H2 production deserves specific characterizations and theoretical modeling for the explanation of the transition phase and energy needed for the adsorption and desorption of propane on top of the palladium atoms. On the other hand, the product distribution will depend on the adsorption and desorption capacity of the different compounds present during the reaction. In this work, the adsorption of propane on a Pd (111) surface was studied by using different approximations. A periodic method based on the Density Functional Theory (DFT) formalism employing vdW-DF functional was investigated for determining preferred binding sites of propane on palladium. The results show that the adsorption on hcp site is more stable than on top site and predictions fit well the experimental results.

Theoretical study of olefin protonation reactions confined inside mordenite zeolite by energy decomposition analysis

The protonation reactions of ethene, propene and isobutene confined inside 8-MR and 12-MR pore structures of mordenite (MOR) zeolite are theoretically studied in order to reveal the origin of different catalytic activity. It is found that the higher activity of propene in 8-MR pore comes from the better fit of dimensional sizes compared to small ethene and bulky isobutene; while in case of large 12-MR pore, the reactivity is enhanced with the increase of molecular size. The interaction energy for the transition state is further investigated by energy decomposition analysis (EDA) method. Two physical properties are shown to highly contribute to the stability of transition state species: the charge property of adsorbed molecules related to the electrostatic interaction and the orbital overlap between adsorbates and zeolite framework involved in the orbital interaction. By using principal components analysis, the major role of electrostatic and orbital interactions in the apparent activation energies were also observed.

Addition and abstraction kinetics of H atom with propylene and isobutylene between 200 and 2500 K: A DFT study

The rate coefficients for the reactions of hydrogen (H) atom with propylene and isobutylene were studied at M06-2X/6-31+G(d,p) and MPWB1K/6-31+G(d,p) level of theories between 200 and 2500K. The possible mechanism for the reactions of propylene and isobutylene with H atom were examined. The rate coefficients for each reaction channels were calculated over a wide range of temperature using Conventional Transition State Theory (CTST). The quantum mechanical tunneling effect was computed using parabolic model and were included in the rate coefficient calculations. The Arrhenius expressions for the reactions, propylene+H and isobutylene+H were estimated to be kpropylene+H=(9.68±0.17)×10−18 T2.16exp[−(131±10)/T]cm3 molecule−1s−1 and kisobutylene+H=(1.40±0.22)×10−16 T1.89exp[−(215±12)/T]cm3molecule−1s−1, respectively. Theoretically calculated rate coefficients are found to be in good agreement with the available experimentally measured rate coefficients.

1, 2‐Epoxy Propane Induced Self‐Assembly of Macroscopic Graphene with Good Adsorption

AbstractA universal and simple one‐step approach to fabricate three‐dimensional (3D) graphene materials with the aid of 1, 2‐epoxy propane (PO) has been reported in this paper. PO, as one of widely used engineering materials, is easy to produce ring‐opening reaction under acidic conditions. When PO is introduced into graphene oxide (GO) dispersion (pH=2.4‐3.8), a 3D graphene architecture will be formed through the reaction of PO with oxygen‐containing functional groups (i. e. epoxy, carbonyl and carboxyl groups) on the surface of GO sheets. The obtained 3D graphene monolithic exhibits high porosity, strong mechanical performance, and good adsorption capacities for oil and organic dyes, which may find potential applications in wastewater treatment, environmental remediation, and electrochemistry.

Dispersed Vanadium in Three-Dimensional Dendritic Mesoporous Silica Nanospheres: Active and Stable Catalysts for the Oxidative Dehydrogenation of Propane in the Presence of CO2.

The uniform monodispersed vanadium-doped three-dimensional dendritic mesoporous silica nanospheres (nV-MSNSs) were successfully synthesized in a heterogeneous oil-water biphase stratification reaction system and characterized by several state-of-the-art methods. The synthesized nV-MSNSs were applied to the oxidative dehydrogenation of the propane (ODHP) reaction with the presence of CO2 and exhibited excellent catalytic performances. The results show that the vanadium loading (1.3-8.0 wt %) evidently influences the textural properties, oxidation state, and polymerization degree of vanadium species of nV-MSNSs. The specific surface area (SBET), pore diameter (Dp), and pore volume (Vp) of nV-MSNSs decrease with the loading of vanadium species. The excessively high vanadium loading leads to the slight connection of nanospheres, but does not affect the assembly and growth of the three-dimensional (3D) dendritic channels. The percentage of highly dispersed vanadium VV species gradually increases and attains the maximum value for 5.2V-MSNSs with the loading of vanadium and then decreases with further vanadium addition. The higher-polymerized VOx species gradually generates above 5.2 wt % vanadium content for nV-MSNSs. The lower-polymerized VOx species appear to be more active than the higher-polymerized VOx species. Markedly, the 5.2V-MSNSs exhibit the highest catalytic activity with the initial propane conversion of 58% for the ODHP. The excellent catalytic performance can be maintained after eight reaction-regeneration cycles. The silica mesoporous frameworks can be well preserved in the reaction-regeneration cycles; meanwhile, the highly dispersed vanadium oxide also can be fully recovered after in situ regeneration. Hence, nV-MSNS catalysts exhibit outstanding activity and stability, and it would have a promising application in the DH of alkanes.

NbOx/CeO2-rods catalysts for oxidative dehydrogenation of propane: Nb–CeO2 interaction and reaction mechanism

A series of NbOx/CeO2-rod catalysts were synthesized and employed as catalysts for oxidative dehydrogenation of propane (ODHP) reaction. Nb–CeO2 interaction and reaction mechanisms were studied with synchrotron-radiation-based techniques. Synchrotron radiation photoemission spectroscopy and resonant photoemission spectroscopy results demonstrate that the Nb5+ precursor preferentially interact with surface oxygen vacancies on CeO2 rods. Surface redox reactions occur between Nb5+ and Ce3+ (surface oxygen vacancy) to produce Nb4+ and Ce4+, resulting in decreased surface oxygen vacancy concentrations on CeO2 rods. CeO2 rods are active in catalyzing propane combustion at low temperatures (below 400°C) via the MvK mechanism. The loading of NbOx suppresses the surface reducibility of CeO2 rods, leading to decreased activity but greatly enhanced propene selectivity. The ODHP reaction catalyzed by CeO2 rods and NbOx/CeO2-rods catalysts at high temperatures (above 450°C) involves the radical mechanism, in which the gas-phase propyl radical was observed with synchrotron radiation VUV photoionization time-of-flight mass spectroscopy. These results greatly deepen the fundamental understanding of CeO2-based catalysts for ODHP reaction.

Polymerization of alkenes with a post‐metallocene catalyst containing a titanium complex with an oxyquinolinyl ligand

ABSTRACTPolymerization reactions of ethylene, propylene, higher 1‐alkenes (1‐hexene, 1‐octene, 1‐decene, vinyl cyclohexane, 3‐methyl‐1‐butene), and copolymerization reactions of ethylene with 1‐octene with a post‐metallocene catalyst containing an oxyquinolinyl complex of Ti and a combination of Al(C2H5)2Cl and Mg(C4H9)2 as a cocatalyst were studied. The catalyst is highly active and, judging by the broad molecular weight distribution of the polymers, contains several active center populations. The active centers differ not only in their kinetic parameters but also in stereospecificity. Most of the active centers produce essentially atactic polypropylene but a small fraction of the centers produces polypropylene of moderate isotacticity degree. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 1844–1854