Pulse Microreactor Research Articles

Insight into induction period of methanol conversion reaction: Reactivity of ethene-precursors over H-ZSM-5 zeolite is independent of Brϕnsted acid site density

A series of H-ZSM-5 (TZ-m, m represents different Si/Al ratios) has been prepared and their Methanol to Olefin (MTO) performance are investigated. By adjusting the catalyst weight of H-ZSM-5 loaded in the pulse micro-reactor, the total Brϕnsted acid sites (BAS) amount of TZ-m catalysts is unified. The resultant similar methanol conversion (∼24 %) over different TZ-m zeolites confirms that the MTO reaction is dominantly catalyzed by BAS. Nevertheless, the BAS density considerably influences the reaction pathways; more condensed BAS enhances the relative propagation of aromatic-based cycle to alkene-based cycle, and vice versa. However, isotopic co-feeding and switching experiment reveals that the reactivity of aromatic hydrocarbon pool (HCP) species, which has been considered as main ethene precursors, is almost independent of acid site density. Although large amounts of aromatics are generated via hydrogen transfer reactions on the sample with high acid site density, most of the confined aromatics function as coke precursors instead of active HCPs. The accumulation of such confined aromatics in zeolite channels further limits olefins mobility and their access to BAS, leading to decreased reactivity of alkene HCPs on high acid site-density samples.

Hydroconversion of n-hexane over Pt-supported on fibrous silica mordenite catalysts: effect of transition metals on acidity and activity

The effect of incorporation of either Zr, Co, Mo or Zn on Pt/HFSM was investigated for the hydroconversion of n-hexane in a pulsed micro-reactor at a temperature range 423-623 K. The acidity of all the studied catalysts were investigated using pyridine adsorption and Fourier Transform Infrared Spectroscopy. The FTIR-pyridine study showed that the catalysts possessed different concentration and strength of both Lewis and Brønsted acid sites. It was revealed that the moderate acid sites distribution on PtZr/HFSM and PtZn/HFSM facilitated the isomerization of the intermediate hexene while the strong acid sites were selective towards cracking reaction. The trend for the bimetallic catalysts studied in n-hexane hydroisomerization is in the order: PtZr/HFSM>PtZn/HFSM>PtMo/HFSM>PtCo/HFSM. The highest activity for hydrocracking and hydrogenolysis were exhibited by PtMo/HFSM and PtCo/HFSM respectively. The PtZr/HFSM exhibited the highest hydroisomerization activity due to the moderate acidity and abundant Lewis acid sites capable of generating protonic acid sites by the hydrogen-spill over phenomena.

Unique structure of fibrous ZSM-5 catalyst expedited prolonged hydrogen atom restoration for selective production of propylene from methanol

A unique mesostructured fibrous silica@ZSM-5 (HSi@ZSM-5) catalyst was synthesized via microemulsion ZSM-5 zeolite seed assisted synthesis method and successfully applied in enhanced propylene formation in methanol to olefin (MTO) process. Characterization of the catalysts were carried out by FESEM, TEM, XRD, TGA, N2 adsorption-desorption, NH3 and KBr probed FTIR. Catalytic performance of as-synthesized catalyst was examined using a micro-pulse reactor and compared with the commercial HZSM-5. The reaction mechanism was elucidated by in-situ methanol FTIR spectroscopy. It was found that HSi@ZSM-5 produced higher propylene selectivity (56%) and was stable for long time on stream (80 h), nearly three-fold higher than that of commercial HZSM-5. In addition, HSi@ZSM-5 displayed higher rate of methanol dehydration, surface methoxy species generation and olefin methylation, indicating that alkene catalytic cycle is the dominant reaction mechanism. The higher selectivity towards propylene was correlated to the existence of moderate acidity which impeded the formation of paraffins and polymethylbenzene intermediates. These observations are further supported by KBr probed FTIR findings which revealed negligible paraffinic carbon species on HSi@ZSM-5. Thus, the unique fibrous silica@ZSM-5 retarded coke deposition due to suppression of undesired side reactions thereby signifying intensified propylene formation, which is highly desirable in commercial MTO processes.

Surface properties enhancement of battery separator by micro-plasma treatments

The aim of this work is to test the wettability enhancement of a low-wetting and low-cost commercial polymer separator by cold microplasma treatments. Liquid and gas ammonia are tested as precursors in a pulsed microreactor at low pressure. Two modes of plasma producing are used, i.e., with and without bias. Optical emission spectroscopy, contact angle technique, and cycling tests are performed to characterize the process and the separator. Best results are obtained with liquid ammonia precursor without bias (contact angle between water and a polyethylene separator being 10° ± 2° compared to 111° ± 2° without any treatment). Cycling tests of lithium half-cells incorporating plasma-treated separator show drastic improvements to capacity retention at high rates (after 100 cycles at a 2C rate, the discharge capacity of a Li4Ti5O12 is almost three times higher, i.e., 38 mA h g−1 and 113 mA h g−1 with an untreated separator and a treated one, respectively).

Ethylene production via catalytic ethanol dehydration by 12-tungstophosphoric acid@ceria-zirconia

The use of renewable raw materials as feedstocks for important industrial chemicals presents a challenge to the scientific community in its pursuit of sustainability. The necessary tasks include the revision of significant processes such as the ethanol-to-olefin process (ETO), and our goal was the production of ethylene. We chose 12-tungstophosphoric acid (HPW) supported on ceria-zirconia mixed oxide (Ce0.8Zr0.2O2, CZ) as a promising catalyst. The structural properties of different loadings of HPW (5–45 wt%) and different support preparation methods were examined, in addition to their activities in the gas-phase dehydration of ethanol. The maintenance of the Keggin structure was proved by infrared spectroscopy (FT-IR), 31P solid-state magic angle spinning nuclear magnetic resonance (MAS NMR) and X-ray diffraction (XRD). Scanning electron microscopy (SEM) images showed a gradual increase in the formation of agglomerates by the HPW coating on the support surface. The reaction products were followed by mass spectra in the interval of 200–400 °C. Multiple catalysts reached 100% ethanol conversion and selectivity for ethylene at low temperatures (200, 250 and 300 °C). A double effect of the support was observed: to disperse the HPW, improving its original low surface area, and to probably facilitate the coke burning process. Tests to determine the lifetime of catalysts (e.g., 26.4% HPW/CZ) performed in a pulsed microreactor coupled to a GC system showed at least 70 h of activity at 300 °C temperature, which demonstrated the potential of these catalysts.

Thermal Decomposition of Potential Ester Biofuels. Part I: Methyl Acetate and Methyl Butanoate.

Two methyl esters were examined as models for the pyrolysis of biofuels. Dilute samples (0.06-0.13%) of methyl acetate (CH3COOCH3) and methyl butanoate (CH3CH2CH2COOCH3) were entrained in (He, Ar) carrier gas and decomposed in a set of flash-pyrolysis microreactors. The pyrolysis products resulting from the methyl esters were detected and identified by vacuum ultraviolet photoionization mass spectrometry. Complementary product identification was provided by matrix infrared absorption spectroscopy. Pyrolysis pressures in the pulsed microreactor were about 20 Torr and residence times through the reactors were roughly 25-150 μs. Reactor temperatures of 300-1600 K were explored. Decomposition of CH3COOCH3 commences at 1000 K, and the initial products are (CH2═C═O and CH3OH). As the microreactor is heated to 1300 K, a mixture of CH2═C═O and CH3OH, CH3, CH2═O, H, CO, and CO2 appears. The thermal cracking of CH3CH2CH2COOCH3 begins at 800 K with the formation of CH3CH2CH═C═O and CH3OH. By 1300 K, the pyrolysis of methyl butanoate yields a complex mixture of CH3CH2CH═C═O, CH3OH, CH3, CH2═O, CO, CO2, CH3CH═CH2, CH2CHCH2, CH2═C═CH2, HCCCH2, CH2═C═C═O, CH2═CH2, HC≡CH, and CH2═C═O. On the basis of the results from the thermal cracking of methyl acetate and methyl butanoate, we predict several important decomposition channels for the pyrolysis of fatty acid methyl esters, R-CH2-COOCH3. The lowest-energy fragmentation will be a 4-center elimination of methanol to form the ketene RCH═C═O. At higher temperatures, concerted fragmentation to radicals will ensue to produce a mixture of species: (RCH2 + CO2 + CH3) and (RCH2 + CO + CH2═O + H). Thermal cracking of the β C-C bond of the methyl ester will generate the radicals (R and H) as well as CH2═C═O + CH2═O. The thermochemistry of methyl acetate and its fragmentation products were obtained via the Active Thermochemical Tables (ATcT) approach, resulting in ΔfH298(CH3COOCH3) = -98.7 ± 0.2 kcal mol-1, ΔfH298(CH3CO2) = -45.7 ± 0.3 kcal mol-1, and ΔfH298(COOCH3) = -38.3 ± 0.4 kcal mol-1.

A gas chromatography/mass spectrometry study of the conversion of alicyclic alcohols on membrane-type catalysts using a pulse microreactor implanted into a gas chromatograph injector

A pulse microreactor implanted directly into a gas chromatograph injector combined with a mass spectrometer has been proposed for monitoring the activity of heterogeneous catalysts. The microreactor was made of a standard commercial liner for a particular gas chromatograph and contained a catalytic bed. A heated injector oven was used simultaneously for heating the catalytic region, rapid evaporation of the substrate, and pulsed introduction of reaction products into a chromatographic column. The temperature of the oven could be varied in the range 200–300°C. The method ensures the detailed description of the qualitative composition of the reaction products. The potential of the proposed microreaction system was demonstrated in the study of membrane-type catalysts (nanodiamonds modified by Pt–Ru and Pt–Ni and also catalytic phosphate systems with NASICON structure) in reactions of cyclohexanol, cyclopentanol, and cyclobutanol. The studied heterogeneous catalysts can be divided in two groups. One group (based on nanodiamonds) promotes dehydrogenation reactions. The NASICON catalytic group catalyzes dehydration reactions with the formation of cycloalkenes and dicycloalkyl ethers.

Pulsed Micro-reactor: An alternative to estimating kinetic parameters of non-catalytic gas–solid reactions

A Pulsed Micro-reactor (PMR) technique is demonstrated as a simple and viable alternative to generate kinetic data for non-catalytic gas–solid reactions. An experimental test rig was designed and fabricated for this purpose. Oxidation of Cu using air and reduction of CuO using methane, encountered in a novel form of combustion known as Unmixed Combustion (UMC), were chosen as representative reactions in this study. Plug flow conditions in the reactor, essential for accurate estimation of kinetic parameters, was confirmed using a Residence Time Distribution (RTD) approach. A simple generic methodology, based on a uniform reaction model is presented which allowed for easy interpretation of data from this reactor system. While the methodology has been validated for both reactions which were prima facie found to be surface reaction controlled, it can easily be extended to pore diffusion limited reactions. The estimated values of reaction orders and activation energies for both reactions and the pre-exponential factor for oxidation were found to be in excellent agreement with those obtained using Thermo Gravimetric Analysis (TGA). A lower value of pre-exponential factor for reduction however was obtained in the present investigation. While the PMR, can provide an initial insight into the reaction mechanism, it can also be used to obtain reaction engineering data related to process development.

Hydride transfer between a phenolic surface pool and reactant paraffins in the catalytic cracking of m-cresol/hexanes mixtures over an HY zeolite

The effect of the presence of m-cresol on the monomolecular and bimolecular pathways of paraffin conversion has been studied over the bare surface of an HY zeolite in a micropulse reactor. The influence of m-cresol is interpreted in terms of the two types of sites present in pristine HY zeolites pretreated at high temperatures. These two types of sites are described as normal Brønsted acid sites and synergistic sites. The latter have higher activity and favor the monomolecular path. They are more severely deactivated than the former by the presence of m-cresol, especially at low reactant concentrations, where the monomolecular reaction is the dominating path. At higher reactant concentrations, hydride transfer from paraffins becomes important and promotes desorption of the phenolic compounds, which hinders the deactivating effect of m-cresol and the growth of a surface phenolic pool, typically formed by condensation reactions of phenolics. Hydride transfer between the paraffinic feed and the surface carbenium ions is also reduced by the presence of m-cresol.

Generation of synergistic sites by thermal treatment of HY zeolite. Evidence from the reaction of hexane isomers

We have studied the conversion of hexane isomers on HY zeolites (Si/Al=40 and 2.6) after different thermal pretreatments (400–600°C) on a micropulse reactor, which is ideal for evaluating catalyst activity and evolution of product distribution over fresh zeolites at very short times on stream, when coke formation is negligible. We have observed that the catalytic activity of the zeolites is enhanced upon high-temperature pretreatment. This activity enhancement can be ascribed to dehydroxylation, as observed by thermogravimetric analysis upon heating the zeolite above 500°C. However, this dehydroxylation does not result in a decrease in the density of the original Brønsted acid sites (BAS). Therefore, the newly created Lewis acid sites (LAS) must be associated with either extra-framework alumina (EFAl) or silanol species. We propose that the activity enhancement is associated with the generation of synergistic sites resulting from the interaction between LAS created by the dehydroxylation and the original BAS. Both, protolytic cracking and dehydrogenation reactions are enhanced with paraffin feeds, but such enhancement is not apparent for olefin feeds. The synergistic sites were also deactivated very quickly by strong adsorption of hydrocarbon species, but could be regenerated by a subsequent high-temperature treatment.

Hydrodechlorination Reactions of CCl4 Over HZSM-5- and HY-Supported Pt and Pd Catalysts

The hydrodechlorination reactions of CCl4 have been studied over Pt/HZSM-5, Pt/HY, Pd/HZSM-5 and Pd/HY under hydrogen atmosphere in the 393–673 K temperature range in a pulse microreactor. The catalysts were prepared by impregnation and were characterised by various physico-chemical means. It has been found that all catalysts were active in the partial to full dechlorination reactions. Typically, over the Pt-containing catalysts methane was the major dechlorinated product, while it was ethane over the Pd-containing catalysts. This latter product predominated over the Pd/HZSM-5 and the quantities of the di- and trichlorinated products were minimal and the monochlorinated one was not formed at all. Phosgene formed was the indication of the partial destruction of the support being more serious for the HY-supported ones.

Distinguishing Enolic and Carbonyl Components in the Mechanism of Carboxylic Acid Ketonization on Monoclinic Zirconia

This study contributes toward understanding the mechanism of catalytic formation of mixed ketones in an attempt to improve their selectivity vs symmetrical ketones. A pulsed microreactor placed inside a gas chromatograph–mass spectrometer instrument was used to identify the source of carbonyl group and quantify its distribution among products of zirconia-catalyzed cross-ketonization reaction of a mixture of carboxylic acids, with the carbonyl group of one of the acids selectively labeled by 13C. A concept of enolic and carbonyl components in the ketonization mechanism was introduced to distinguish the sources of alkyl and acyl groups, respectively. The least branched acid was found to be the predominant source of CO2, the essential byproduct of ketonization. Thus the least branched acid is the preferred source of the alkyl group of the cross-ketone product, while the most branched acid provides the acyl group. Increased branching at the α carbon next to the carbonyl group decreased the reactivity of both ...

Electronic effects in the coke deactivation of platinum-alumina catalysts

By means of XPS, ESR, DTA, and pyridine flash desorption techniques; micropulse reactor studies; and quantum-chemical calculations, it was shown that, during the coking of platinum-alumina catalysts in hydrocarbon media, the electron density of the platinum atom increases up to the formation of Pt0, which is a deactivating factor from the viewpoint of the electronic effects. The stabilization of the activity of platinum-alumina catalysts consists in an increase in the effective positive charge on the platinum atom; this function is fulfilled by modifier elements. It was found that the platinum protection mechanism differs, depending on the nature of the modifying additive: certain elements function via another, additional mechanism of catalyst stabilization, the blocking action. The theoretical conclusions made in this study are corroborated by the results of testing a new, Pt-Sb-Re catalyst supported on Al2O3-Cl with predicted properties.

Comparison of the Hydrocarbon Yield from Methanol Conversion with Different Catalysts

Methanol conversion over two FCC catalysts, β zeolite catalyst, fresh ZRP catalyst series, and fresh SAPO-34 catalyst was experimentally investigated, and the methanol conversion between those catalysts was compared over pulse micro-reactor under 500°C. The effect of different temperatures on the products distribution over SAPO-34 catalyst, first with pure methanol feed and then with methanol/water mixture feed, has been studied. Pulse-micro-reactor and FID gas chromatograph equipment were used. Experimental results indicate different catalysts have different effects on methanol conversion, light olefins yield increased and DME decreased when using SAPO-34 catalyst as the temperature was increased. The optimum temperature appears to be 450°C in terms of methanol conversion to light olefins over SAPO-34.

In situ IR and catalytic studies of the regeneration of acid sites in coked zeolite Y

The process of regeneration of zeolite catalyst by coke oxidation was followed by “in situ” experiments in which the coke deposition, and subsequently coke oxidation were carried out inside flow IR cell. The characterization of acid sites by ammonia sorption and desorption, as well as by CO sorption, was done also in the same IR cell without exposing the sample to the air. The information on the nature of OH groups was obtained by recording the spectra at low temperature (170 K) which narrows IR bands and improves resolution. The effect of coke deposition and regeneration on catalytic properties of zeolite was studied in the experiments in which coke deposition and zeolite regeneration were carried out inside IR cell (the properties of such zeolite were characterized by IR spectroscopy) and afterwards zeolite was transmitted to a pulse microreactor and catalytic test was realized. Coke deposition eliminated some hydroxyls (most acidic ones were eliminated the first): IR bands diminished, concentration and acid strength of OH groups decreased. As a consequence, catalytic activity in m-xylene reaction decreased too. Oxygen treatment at 720 K decreased IR bands of coke by ca. 40% but all protonic sites became able to protonate ammonia and became active in m-xylene reaction. However, OH bands which decreased by coke deposition restored their intensity only a little, suggesting that some protonic sites (of relatively low acidity) were “invisible” in IR spectra as OH groups, they were still able to protonate ammonia and to be active sites in m-xylene reaction.

Interaction of water with titania and zirconia surfaces

Isotopic exchange of water on the surface of monoclinic zirconia and the anatase form of titania was studied experimentally using an ordinary gas chromatograph/mass spectrometer (GC/MS) as a pulse microreactor. Interaction of water with these surfaces was modeled by first principles calculations for periodic structures within density functional theory. Experimental data support computational results showing dissociation of water on monoclinic zirconia's most stable surfaces ( 1 ¯ 1 1 ), ( 1 ¯ 0 1 ) and (1 1 1). Water is adsorbed molecularly on the anatase (1 0 1) surface and dissociatively on the anatase (1 0 0) surface. Interaction of water with the anatase (0 0 1) surface proceeds through insertion into a Ti O bond. By monitoring the concentration of the mixed water isotope, DHO, during the isotopic exchange of surface water with D 2O, it was found that exchange of water on anatase surfaces at 200–400 °C proceeds by whole molecules from 30% to 70% depending on the temperature and the surface coverage. In contrast, water exchanges on zirconia by single hydrogen atoms with a complete scrambling of hydrogens, at least 99%, under the same conditions. The proposed mechanism of water exchange on zirconia surface includes interaction through hydrogen bonding between hydroxyl groups adsorbed on neighboring sites. The observed anomaly on anatase is in agreement with the preferential molecular adsorption on a (1 0 1) surface and with the insertion of water into Ti O bonds on a (0 0 1) surface. This study contributes to the understanding of the atomic structure of acid–base catalytic sites on anatase titania and monoclinic zirconia surfaces.

The activity of Au supported on various types of carbon in the ring transformation reactions of methyloxirane

In this work the catalytic activity of gold catalysts supported on various forms of carbon is described and compared in the ring transformations of propylene oxide (methyloxirane). The catalysts were Au/multiwall carbon nanotube (Au/MWNT), Au/activated carbon and Au/graphite. The reactions were studied in a pulse microreactor in the 363 - 473 K temperature range. Methyloxirane underwent deoxygenation and isomerisation over the Au/MWNT and Au/activated carbon catalysts but deoxygenation only occurred over Au/graphite. At 363 K the Au/MWNT was only active, and it proved to be the most active catalyst at each temperature. This finding was attributed to an optimum mix of defect sites at the metal-support interface and electric conductivity of the support - both believed to be crucial in the high catalytic activity observed.

Combustion of trichloroethylene and dichloromethane over protonic zeolites: Influence of adsorption properties on the catalytic performance

The deep oxidation of dichloromethane (DCM) and trichloroethylene (TCE) over protonic zeolites (HA, HX, HY and H-ZSM-5) was studied in this work. Experiments were performed in dry air in the range 50–650 °C in a pulsed microreactor. Catalytic activity was correlated with the capacity of adsorption of DCM and TCE as well as the strength and specificity of these interactions, which parameters were determined by inverse gas chromatography (IGC). DCM is oxidized at lower temperatures than TCE, and at the same time, the interaction of this compound over the catalysts is also stronger than that of TCE. The increase of the TCE conversion in presence of the catalysts was very low, whereas these materials (specially the HY and H-ZSM-5 zeolites) have important catalytic activity for DCM oxidation. The best performance of these zeolites has been attributed to the higher density of strong acid sites, which act as active sites both in the adsorption of hydrocarbon and catalytic activation of hydrocarbon halides. The product distribution is also discussed in this work.

Catalytic combustion of hexane over transition metal modified zeolites NaX and CaA

Hexane deep oxidation was studied over NaX and CaA zeolites modified by ion exchange with transition metals (Mn2+, Co2+, Fe3+), the percentage of ion exchanged, determined by ICP-MS, varying between 39 and 98%. Parent and exchanged zeolites were characterized by X-ray diffraction (XRD), N2 physisorption, temperature-programmed reduction (TPR), oxygen and ammonia temperature-programmed desorption (TPD) and inverse gas chromatography (IGC). Catalytic activities were evaluated through the recording of light-off curves in a pulsed microreactor, catalytic activity being correlated with physicochemical properties of the solids (crystallinity, surface acidity, adsorption properties and morphological parameters). As general trend, CaA zeolites are more active than NaX zeolites. Mn-exchanged CaA zeolite was the most active catalyst for hexane oxidation, whereas the addition of Fe to the zeolites leads to strong chemical and morphological changes in the parent zeolite.

The Effect of Acidity on Olefin Aromatization over Potassium Modified ZSM-5 Catalysts

The transformation of olefin to aromatics over ZSM-5 catalysts with different K-loadings has been investigated both in a continuous flow fixed-bed reactor and in a pulse microreactor. Investigation of variation of olefin aromatization activity with K-loadings shows that strong acid sites are indispensable for the converting of olefin to aromatics. As intermediates of olefin aromatization process, butadiene and cyclopentene not only show much higher aromatization activity than mono-olefins, but also can be transformed into aromatics over relatively weak acid sites of K/ZSM-5. A proposal is put forward, stating that among all the steps experienced in olefins aromatization, the formation of diene or cycloolefin from mono-olefins through hydrogen transfer is the key step and can be catalyzed by strong acid sites.