Propylene In Presence Research Articles

Catalytic activity and thermal stability of Au–CuO/SiO2 catalysts for the low temperature oxidation of CO in the presence of propylene and NO

Oxidation catalysts in emissions control systems generally contain Pd/Pt and require exhaust temperatures above 200°C to operate, but under low-temperature conditions, oxidation of CO and hydrocarbons are challenging. As engine efficiency improves and exhaust temperature decreases, there is an increasing demand for high emissions control performance at low temperatures. Therefore, it becomes imperative to design new catalysts that are active at low operating temperatures. Au–CuOx catalysts, made through the oxidation of AuCu alloy nanoparticles, have been found to be highly active for the oxidation of CO at low reaction temperatures. The catalytic activity for the conversion of CO using Au–CuOx/SiO2 was evaluated under simulated lean exhaust conditions (CO, C3H6, NO, H2O, O2 and Ar). It was found that the oxidation of CO over the Au–CuOx/SiO2 catalyst was inhibited when C3H6 or NO was introduced into the reaction stream. Interestingly, a physical mixture of Au–CuOx/SiO2 and Pt/Al2O3 worked in synergy to enhance the oxidation of NO to NO2 with 90% conversion near 300°C in the presence of CO. This reactivity is on par with Pt/Al2O3 NO oxidation activity in the absence of CO. The Au–CuOx/SiO2 catalysts were also found to be thermally stable after being aged up to 700°C for 10h. The resistance to particle sintering can be attributed to the CuOx “anchoring” the Au particles to the silica support.

Bayesian decoding of the ammonia response of a zirconia-based mixed-potential sensor in the presence of hydrocarbon interference

Zirconia-based mixed-potential sensors are a promising technology for monitoring levels of nitrogen oxides and ammonia in diesel engine exhaust. However, in addition to the target gases these sensors react to unburned hydrocarbons present in the gas mixture. The observed cross-interference between target and non-target gases cannot be fully mitigated by applying different bias currents to the sensor. On the other hand, sensor sensitivity and selectivity toward various components of the mixture depend on the bias current setting, allowing us to effectively create an array of sensors by applying different bias currents to the same device. Here we show how such an array can be used to predict absolute concentrations of ammonia in the presence of propylene. Our Bayesian framework can be easily generalized to other types of sensors and to more complex chemical mixtures. It consists of two steps: the calibration step, in which the parameters of the model are determined a priori in the laboratory setting, and the prediction step, which mimics the deployment of the device in real-world conditions. We investigate a linear model, in which response of the sensor to each gas is assumed to be additive, and a nonlinear model, which takes interference between gases into account. We find that the nonlinear model, although more complex, yields more accurate predictions. We also find that relatively few sensor readings and bias current settings are required to make reliable predictions of gas concentrations in the mixture, making our approach feasible in a variety of automotive and other technological settings.

The Effect of Noncatalytic Cations on the Activity and Selectivity of Nickel-Exchanged X Zeolites for Propene Oligomerization

A series of alkali metal or alkaline earth-exchanged NiX (X=faujasite zeolite, Si/Al=1.2) zeolites containing approximately 0.6 wt % Ni as Ni2+ cations were examined as catalysts for propene oligomerization at 453 K and 5 bar (500 kPa). In the presence of propene, the activity of alkali metal-exchanged zeolites (NiLiX, NiNaX, and NiKX) increased with time on stream, reached a maximum, then decreased, and finally reached steady state. In contrast, the activity of alkaline earth-exchanged zeolites (NiMgX, NiCaX, and NiSrX) was high initially and then decreased until steady-state activity was achieved. The primary product formed in all cases was hexene (90 %), and nonene was the only other product observed (10 %). Both the rate of propene dimerization and the ratio of branched to linear hexene isomers were determined to depend on the identity of the charge-compensating cation, with the dimerization rate and degree of dimer branching increasing with increasing free volume in the zeolite supercages. The apparent activation energy for trimer formation was greater than that for dimer formation, which suggests that steric constraints imposed by the zeolite may inhibit the growth of larger oligomers.

Selectively combusting CO in the presence of propylene

Acrylic acid plant capacity can be increased by 30% by substituting propane for nitrogen (in air) thereby increasing the overall gas heat capacity. To minimize propane purge rates, the effluent is recycled but the CO in the recycle stream must be oxidized to avoid poisoning the catalyst. We studied the kinetics of CO combustion in a micro-fluidized bed with a catalyst inventory of 1g and a 4cm ID reactor charged with 5g of catalyst – Pd/zeolite – and 145g of inert. Experiments were run at temperatures between 90 and 240°C and at 1 and 3.2 bara. At temperatures below 140°C propylene conversion was less than 30% while CO conversion approached 90% at gas hourly space velocities near 10,000h−1. A first order kinetic model characterized the data over the whole range of conditions in which conversion was varied between 2% and 99+%. The rate constant for CO conversion was equal to 0.75s−1 whereas it equaled 0.04s−1 for propylene oxidation; the activation energy for CO oxidation was 95kJmol−1K−1 whereas it was 140kJmol−1K−1 for propylene.

Catalytic behavior of Ni-modified perovskite and doped ceria composite catalyst for the conversion of odorized propane to syngas

The catalytic activity of a Ni-modified perovskite (LSFCO) — ceria doped gadolinia composite catalyst in the presence of odorized propane has been studied in order to assess this material as catalyst for a fuel processor in Solid Oxide Fuel Cells (SOFCs). At first, the study involved the investigation of the catalytic activity in the presence of propane in different reaction conditions and temperatures. Once established the best reaction conditions, the catalytic stability in an endurance test, and subsequently the effect on the catalytic performance of adding different amounts of H2S, has been explored. The autothermal reforming (ATR) at 800°C has provided the highest performance (99% C3H8 conversion, 67% H2 and 17% CO yields). The upper limit of H2S content in propane for which the performance of such catalyst is still acceptable in terms of propane conversion and syngas yield is 80ppm. Accordingly, the level of sulfur contaminants tolerated by this catalyst is much higher than that of conventional Ni-based catalyst for similar conversion and syngas yield.

Phase equlibiria and diffusivity of dense gases in various polyethylenes

The aim of this work was to investigate the properties of polyethylenes (PE) of various densities (low-density and high-density) under pressure of CO2 and propane. The phase equilibria of PE of different density in presence of CO2 and in presence of propane in dependence of pressure and temperature were investigated. The phase transitions of PE at atmospheric pressure were determined by differential scanning calorimetry (DSC). Furthermore, phase transitions of polymers under pressure of gases were measured by using an optical high pressure cell. Measurements of phase transition were performed in range of pressure of 1–90MPa. The results show that melting points of LDPE decreased in presence of CO2 and in presence of propane. For high-density polyethylene (HDPE) the melting point decrease was observed only in presence of propane, while in presence of CO2 melting point increases with increasing pressure. The melting points of LDPE and HDPE decrease in average for 10–20K in presence of propane, while in presence of CO2 the melting point decrease for both LDPE was lower (5–10K). Solubility and diffusivity of supercritical CO2 in two low-density polyethylenes (LDPE) and in high-density polyethylene (HDPE) were measured at temperature 373K and pressures up to 30MPa using a magnetic suspension balance (MSB). The solubility data were used for estimating the binary diffusion coefficients. The solubilities increased with increasing density. The diffusion coefficient shows strong CO2 density and CO2 solubility dependence. Diffusion coefficient starts to decrease with increasing density and solubility of CO2.

Transition from two-stage to direct melt-crystallization in isotactic random butene-1/propene copolymers

The kinetics of crystallization of isotactic polybutene-1 has been investigated as a function of the concentration of propylene chain defects between 0 and 20 mol% by temperature/time-resolved wide-angle X-ray scattering during slow cooling of the melt followed by annealing at ambient temperature. Slow cooling of the melt of the homopolymer leads to formation of Form II mesophase which then transforms on isothermal annealing at ambient temperature to Form I crystals within a period of 10–20 days. Presence of propylene co-units/chain defects in polybutene-1 leads to a retardation of Form II mesophase formation on cooling and simultaneously an acceleration of the mesophase–crystal phase transformation. In random butene-1/propylene copolymers containing about 7 mol% propylene crystallization is completed in less than a day. For copolymers with more than 7 mol% propylene, Form I crystals develop by both reorganization of Form II mesophase and directly from the melt. The study is completed by evaluation of the effect of copolymerization on the crystallinity and crystal perfection.

SO2 oxidation and nucleation studies at near-atmospheric conditions in outdoor smog chamber

Environmental context Nucleation, a fundamental step in atmospheric new-particle formation, is a significant source of atmospheric aerosols. Most laboratory experiments investigate H2SO4 nucleation based on indoor chambers or flow tube reactors, and find discrepancies with field observations. Here a large outdoor smog chamber is used to study the relationship between SO2 and nucleation rates, and demonstrate the importance of aqueous phase oxidation of SO2 by H2O2 and other oxidants. Abstract Particle formation under different initial ambient background conditions was simulated in a dual outdoor smog chamber for the SO2 and O3–SO2 systems with and without sunlight, as well as a propylene–NOx–SO2–sunlight system. An exponential power of 1.37 between nucleation rates at 1nm (J1) and SO2 gas phase concentrations was obtained for the SO2–sunlight system and a minimum of 0.45ppbSO2 is required by this relationship to initiate nucleation (J1 is equal to 1cm–3s–1). An investigation of the O3–SO2–sunlight/dark system showed that the presence of O3 contributed to the particle nucleation and growth at night; however, it only enhanced the particle growth in the daytime when H2SO4 photochemistry was present. In the presence of an OH• scavenger, the O3–SO2 system did not show particle nucleation, suggesting that the scavenger cut off this pathway of SO2 oxidation. A lower nucleation rate and higher particle grow rate were also observed for SO2 oxidation in the presence of propylene and NOx. However a higher SO2 decay rate was obtained for the propylene system especially under high relative humidity, which was not observed in the O3–SO2 system. This suggests that aqueous phase oxidation of SO2 from H2O2, RO2• and other oxidants produced in the propylene–NOx system contribute to the particle growth.

Synthesis and Ring-Opening Metathesis Polymerization of Norbornene-Terminated Syndiotactic Polypropylene

Using nonliving bis(phenoxyimine)titanium catalysts activated by methylaluminoxane (MAO) in the presence of propylene, allyl-terminated syndiotactic polypropylene macromonomers with varying tacticity ([rrrr] = 0.80 and 0.94) and molecular weight (Mn = 3600 and 5600 g/mol) were produced. The end-functionalized polymers were converted to hydroxyl- and subsequently norbornene-terminated macromonomers. Two series of syndiotactic polypropylene comb-polymers were synthesized through metathesis polymerization of the norbornene-functionalized polypropylene. The molecular weight (Mn = 46 000–172 000 g/mol) and polydispersity (Mw/Mn = 1.21–1.89) of the comb polymers was determined by gel permeation chromatography (GPC). Using differential scanning calorimetry (DSC), melting temperature (Tm) and crystallization temperature (Tc) were determined and both were observed to decrease with increasing conversion to poly(macromonomer). To the best of our knowledge, this is the first synthesis of comb-polymers from end-functionalized syndiotactic polypropylene.

Effective electrocatalytic reduction of propene at a Pt electrode in strongly acidic solutions with Mo(VI) oxo-species

An appreciable enhancement of the rate of propene electroreduction was discovered under CV conditions on a polycrystalline Pt electrode in a strongly acidified solution containing cationic Mo(VI) oxo-species. Simultaneously, the electroreduction of these species was found to be remarkably more effective in the presence of propene in comparison with that obtained using a supporting electrolyte without the alkene. Evidence was provided that the catalytic effect results from the continuous regeneration of the electroactive molybdenum moieties via a non-faradaic reaction between propene and the reduced forms produced at the electrode/solution interface from the parent Mo(VI) cationic species in the preceding one and three electron-transfer reactions.

Nanocomposite MFI-Alumina Hollow Fiber Membranes: Influence of NOx and Propane on CO2/N2 Separation Properties

This study provides a detailed survey of the effect of moisture, NOx and light hydrocarbons (i.e., propane) on the CO2/N2 permeation and separation properties of MFI-type hollow-fiber membranes in view of on board CO2 capture applications in Diesel vehicles. Five different MFI-alumina samples have been prepared including different degrees of isomorphous boron and germanium substitution, as well as ex framework proton exchange by copper. The quality of the synthesized hollow fibers has been primarily assessed by pure N2 permeation and n-butane/H2 and SF6/N2 separation at room temperature. The different materials show preferential CO2/N2 and CO2/NO selectivity at low CO2 feed concentrations (∼10%) in the temperature range 298–373 K, which can be appreciably promoted under the presence of propane (1 v/v %). The materials show stable and high CO2 permeances even in the presence of large amounts of water in the feed stream. On the basis of the permeation and separation data measured in this study, we present a refined simulation study of a membrane cascade system constituted of two hollow-fiber membrane modules coupled to a DeNox unit for on board CO2 capture and liquefaction/supercritical storage in heavy vehicles (>40 tn).

Effects of noble metal addition on response of ceria thick film CO sensors

Abstract Cerium oxide (ceria) CO sensors exhibit fast, but smaller response than tin dioxide CO sensors; therefore, improvement in the response of ceria CO sensors is required. The effects of noble metal addition (Pt, Ag, Pd, or Au nanoparticles) on the response of ceria thick film CO sensors were investigated. The ceria thick film sensors with Au nanoparticles exhibited good response to CO; the addition of 5 wt% Au caused a 40 times increase in the sensor response. In contrast, no change in response was observed for the addition of Au to tin dioxide sensors. The response of the ceria sensors with Au decreased in the presence of propane or ethane compared to that without the noble metal. The sensors with Ag nanoparticles showed an increase response in the first measurement, but this response decreased with each measurement. Pd addition to the ceria sensors resulted in uneven responses and no increase in resistance was observed, in contrast to the tin dioxide sensors of which the resistance increases by Pd addition. In the case of the ceria sensors with Pt nanoparticles, the response was approximately the same as the sensors without noble metal nanoparticles.

Support effects on catalytic performance for selective combustion of hydrogen in the presence of propene

γ-Al2O3, α-Al2O3 and SiO2 have been employed as the supports of Pt catalysts for the process of selective hydrogen combustion (SHC) in the presence of propene at high temperature. High H2 conversion can be obtained over different catalysts being accompanied with a considerable amount of C3H6 consumption. But the oxidation of C3H6 to CO and CO2 keeps under a low level over all catalysts. An A factor has been introduced to evaluate the priority of H2 conversion over C3H6 conversion given by the catalysts. The results show that the Pt catalyst supported on α-Al2O3 with 1.6wt.% Pt loading can bring about the highest value of A factor among all catalysts. But γ-Al2O3 is not a proper support in terms of A factor. The support effect has been studied on the basis of characterization of physicochemical properties of the supports and the catalysts by means of BET, NH3-TPD, TG, TPR and TEM techniques. The results reveal that the support with lower specific surface area and lower acidity is of help to generating larger Pt particles with less interaction with the support, thus being beneficial to the diminishment of C3H6 consumption. The H2 combustion selectivity can be improved accordingly.

Propene Poisoning on Three Typical Fe-zeolites for SCR of NOx with NH3: From Mechanism Study to Coating Modified Architecture

Application of Fe-zeolites for urea-SCR of NO(x) in diesel engine is limited by catalyst deactivation with hydrocarbons (HCs). In this work, a series of Fe-zeolite catalysts (Fe-MOR, Fe-ZSM-5, and Fe-BEA) was prepared by ion exchange method, and their catalytic activity with or without propene for selective catalytic reduction of NO(x) with ammonia (NH(3)-SCR) was investigated. Results showed that these Fe-zeolites were relatively active without propene in the test temperature range (150-550 °C); however, all of the catalytic activity was suppressed in the presence of propene. Fe-MOR kept relatively higher activity with almost 80% NO(x) conversion even after propene coking at 350 °C, and 38% for Fe-BEA and 24% for Fe-ZSM-5 at 350 °C, respectively. It was found that the pore structures of Fe-zeolite catalysts were one of the main factors for coke formation. As compared to ZSM-5 and HBEA, MOR zeolite has a one-dimensional structure for propene diffusion, relatively lower acidity, and is not susceptible to deactivation. Nitrogenated organic compounds (e.g., isocyanate) were observed on the Fe-zeolite catalyst surface. The site blockage was mainly on Fe(3+) sites, on which NO was activated and oxidized. Furthermore, a novel fully formulated Fe-BEA monolith catalyst coating modified with MOR was designed and tested, the deactivation due to propene poisoning was clearly reduced, and the NO(x) conversion reached 90% after 700 ppm C(3)H(6) exposure at 500 °C.

A non-NH3 pathway for NOx conversion in coupled LNT-SCR systems

NOx storage-reduction experiments were performed using a coupled LNT-SCR system consisting of a low-precious metal loaded Pt/Rh LNT catalyst and a commercial Cu–zeolite SCR catalyst. Cycling experiments revealed that when a CO+H2+C3H6 mixture or C3H6 by itself was used as the reductant, the NOx conversion over the SCR catalyst exceeded the conversion of NH3 over the same catalyst. This is explained by the presence of propene, which slipped through the LNT catalyst and reacted with the LNT NOx slip. Separate experiments, conducted under continuous flow and lean-rich cycling conditions, confirmed the ability of propene, as well as ethene, to function as a NOx reductant over the SCR catalyst. Cycling experiments also revealed that the SCR catalyst was able to store propene, such that NOx reduction by stored propene continued into the lean phase (after the switch from rich conditions). According to adsorption experiments, significant co-adsorption of NH3 and propene occured in the SCR catalyst, while under lean-rich cycling conditions the contributions of NH3 and C3H6 to NOx conversion were found to be essentially additive. These findings suggest that under actual driving conditions, NOx reduction by non-NH3 reductants (olefins and possibly other hydrocarbons) in the SCR catalyst can contribute to the mitigation of lean and rich phase NOx.

Kinetic modeling of the total oxidation of propane over Cu- and Ce-based catalysts

The mechanism of the total oxidation of propane over alumina supported CuO, CeO 2, and CuO–CeO 2 is studied by means of Temporal Analysis of Products in the temperature range 623–873 K. A reaction scheme is proposed for the total oxidation of propane with O 2, as well as for the separate reduction and oxidation steps. For the reduction of the catalyst with propane, four elementary steps are considered as kinetically significant: (1) reversible associative propane sorption, (2) irreversible dissociative propane adsorption involving a methylene C–H bond breaking and ultimately forming CO 2 *,s, (3) desorption of CO 2 *,s to CO 2, and (4) dissociation of CO 2 *,s to CO *,s and O *,s, and recombination of CO *,s and O *,s to CO 2 *,s. For the oxidation of the catalyst with O 2, two elementary steps are considered as kinetically significant: (1) reversible dissociative adsorption of O 2 on two reduced active sites and (2) diffusion of lattice O atoms from the surface to the bulk and vice versa. An adequate description of the full mechanism, i.e., in the presence of propane and O 2, can only be obtained by considering additional steps, which distinguish between lattice oxygen atoms at the surface, O *,s, and weakly bound oxygen atoms, O weak. Apart from estimating the different kinetic parameters, a new approach to determine the initial concentration of reduced active sites is presented. CuO–CeO 2/γ-Al 2O 3 is a more efficient total oxidation catalyst than the corresponding single metal oxides. The activation energy for the first C–H bond activation in propane over the CuO–CeO 2/γ-Al 2O 3 amounts to 62 kJ mol −1 and is significantly lower than the activation energies over the single metal oxides, i.e., 95 kJ mol −1 for CuO/θ-Al 2O 3 and 126 kJ mol −1 for CeO 2/γ-Al 2O 3. The redox activity of CuO–CeO 2/γ-Al 2O 3 is created by the ability to reduce and re-oxidize both CuO and CeO 2, which is enhanced by a strong interaction between these phases.

Role of NOδ+ Intermediates in NO Reduction with Propene over NiZSM-5 Zeolite Revealed by EPR and IR Spectroscopic Investigations and DFT Modeling

Adsorption at variable temperatures of individual components (NO, NO2, CO, O2, C3H6) and their mixtures simulating the feed of the selective catalytic reduction (SCR) of NOx with propene over NiZSM-5 catalysts was investigated by electron paramagnetic resonance, infrared, and mass spectroscopies to provide direct insights into the nature of the primary reaction intermediates and alternation of the valence state of the nickel centers. The key intermediates ({Ni–NO}2+, {Ni+–C3H6}, {Ni+–(CO)n}, and {Ni2+–O2–}) relevant to the SCR process were isolated and identified, and their structure together with spectroscopic signatures were ascertained by parallel density functional theory molecular modeling. Alternation of the nickel valence state during the SCR reaction, leading to formation of a Ni2+/Ni+ redox couple, was triggered by the reductive adsorption of NO and oxidative adsorption of O2. The sequence at which the reactant molecules were reactively coordinated was dictated by the oxidation state of the nickel centers. It was shown that the SCR process is initiated by chemoselective capture of NO from the reaction mixture by oxidized nickel sites. Concerted spin-pairing and ligand-to-metal charge-transfer events involved in this process lead cooperatively to the formation of nickel-bound nitrosonium (NOδ+) species as the prime intermediate. At SCR temperatures (above 673 K), NOδ+ in the presence of propene and dioxygen is readily converted into N2, COx, and H2O, the final products of the SCR reaction.

Catalytic oxidation of toluene over binary mixtures of copper, manganese and cerium oxides supported on γ-Al2O3

The catalytic oxidation of toluene has been investigated over binary mixtures of copper, manganese and cerium oxides supported on high surface area γ-Al2O3 in comparison with the corresponding single metal oxide components. Catalysts were synthesized with the impregnation method and were characterized with respect to their specific surface area (BET method), phase composition and mean crystallite size (XRD technique), reducibility (H2-TPR) and adsorption/desorption characteristics toward toluene (TPD followed by TPO). Results obtained using a feed composition consisting of 1000ppm toluene in air showed that the catalytic performance of mixed oxide catalysts can be improved significantly by proper selection of metal oxide (MxOy) loading and composition. The intrinsic activity of optimized catalysts, measured under differential reaction conditions, was found to be significantly higher compared to that of their single-component counterparts. This has been attributed to the better dispersion of the active MxOy phases, their increased reducibility (reactivity of surface oxygen), and their lower tendency to form coke deposits under reaction conditions. Addition of a second VOC (propane) or water vapor in the feed affected differently the activity of optimized-mixed oxide catalysts. As a general trend, inhibition by the presence of propane was more pronounced for CeO2-containing samples whereas the presence of H2O affected mainly the CuOx-containing catalysts. It is concluded that the VOC oxidation activity of Al2O3-supported mixed oxide catalysts is determined by the reducibility of the dispersed active phases, which may be controlled by proper selection of MxOy nature, loading and composition.

Adsorptive desulfurization of propylene derived from bio-ethanol

We studied adsorption characteristics of a series of LTA zeolite as an adsorbent for desulfurization of propylene, that was produced from bioethanol by ethanol-to-olefin (ETO) conversion. A breakthrough curve (BTC) for adsorption of methanethiol, as one of the sulfur impurities of propylene produced from bioethanol, in the presence of propylene was measured using a fixed-bed column packed with the LTA zeolite. The BTC revealed that the effect of the competitive adsorption of propylene on the LTA zeolite strongly depended on a cation species exchanged in the micropores of the zeolite. Among the cation species examined in this study, bivalent cation of zinc (Zn2+) was proved to be the most effective one to increase the amount of methanethiol adsorbed on the LTA zeolite under the presence of propylene. The specific interaction of methanethiol with the LTA zeolite exchanged with Zn2+ was confirmed by the measurement of a temperature-programmed desorption (TPD) spectrum of methanethiol.

Hydrogen production by propylene-assisted decomposition of methane over activated carbon catalysts

Catalytic decomposition of methane (CDM) permits obtaining hydrogen in high yields and – what is essential – it does not lead to release of CO 2. Unfortunately, most of the catalysts used in this process undergo fast deactivation. Their possible regeneration, consisting in the removal of pore blocking carbonaceous deposit of low catalytic activity, leads to generation of undesirable carbon dioxide. An alternative solution for maintaining high catalyst activity in the CDM reaction can be generation of the catalytically active carbonaceous deposit on its surface. Such a deposit can be obtained by decomposition of different organic substances. This paper reports on methane decomposition carried out in the presence of propylene (used in the concentration of 10 or 20%). The reaction was performed at three temperatures of 750 °C, 850 °C or 950 °C. Three types of activated carbon were tested as catalysts: the first one was obtained by activation of pine wood biomass with Na 2CO 3, whereas the second and third ones were commercial carbons (WG-12 and Norit RX3 Extra). According to the results, the addition of propylene to the CDM system effectively reduces deactivation of the activated carbon catalysts and permits fast stabilisation of their catalytic activity at a high level.