Conversion Of Olefins Research Articles

Mo oxide supported on sulfated hafnia: Novel solid acid catalyst for direct activation of ethane & propane

Shale gas revolution has opened opportunities for conversion of light alkanes to value-added chemicals like ethylene and propylene. Literature suggests the use of bifunctional catalyst, consisting of a solid acid such as HZSM-5 and a metal oxide for direct conversion [7]. Here, we demonstrate a catalyst consisting of a novel Mo oxide-doped sulfated hafnia (SH) solid acid to convert ethane and propane.Mo-SH was synthesized via impregnation and characterized using BET, XPS, SEM-EDS, DRIFTS, NH3-TPD, XANES and TPO. Catalyst acidity was measured with NH3-TPD and DRIFTS. SEM-EDS and XPS were used to ensure the target loading of Mo on SH. XANES showed that Mo oxides are converted to Mo carbides with time, which are known as the active sites for dehydrogenation, the initial reaction step. Selectivity for ethane is 40–50 % to ethylene and for propane is 70–90 % to propylene at 550−600°C.No significant deactivation was observed for ∼16 h on stream.

Regioselective Hydroformylation of Internal and Terminal Alkenes via Remote Supramolecular Control.

Regioselective catalytic transformations using supramolecular directing groups are increasingly popular as it allows for control over challenging reactions that may otherwise be impossible. In most examples the reactive group and the directing group are close to each other and/or the linker between the directing group is very rigid. Achieving control over the regioselectivity using a remote directing group with a flexible linker is significantly more challenging due to the large conformational freedom of such substrates. Herein, we report the redesign of a supramolecular Rh-bisphosphite hydroformylation catalyst containing a neutral carboxylate receptor (DIM pocket) with a larger distance between the phosphite metal binding moieties and the DIM pocket. For the first time regioselective conversion of internal and terminal alkenes containing a remote carboxylate directing group is demonstrated. For carboxylate substrates that possess an internal double bond at the Δ-9 position regioselectivity is observed. As such, the catalyst was used to hydroformylate natural monounsaturated fatty acids (MUFAs) in a regioselective fashion, forming of an excess of the 10-formyl product (10-formyl/9-formyl product ratio of 2.51), which is the first report of a regioselective hydroformylation reaction of such substrates.

Olefin esterification on Amberlyst® 15 catalyst: does the esterification site defy thermodynamics?

Kinetics for the reaction between 1-tetradecene and heptanoic acid to make tetradecyl heptanoates on dry Amberlyst® 15 catalyst at 90 °C are extremely complex. Observed kinetics of simultaneous double bond isomerization and esterification cannot be reconciled with a single type of catalytic site. Esterification and most of the double bond isomerization must occur on separate sites. Relative rates of esterification for tetradecene isomers suggest that adsorption coefficients on the esterification sites follow 1-tetradecene > 2-tetradecene > 3+-tetradecenes. These relative adsorption coefficients imply that, on this esterification site, 2-tetradecene isomerizes to 3-tetradecene faster than 3-tetradecene isomerizes to 2-tetradecene or 4-tetradecene, a truly novel finding not previously reported for any other acidic site. The site where most of the double bond isomerization occurs does not display this behavior, and isomerization of linear tetradecenes proceeds to thermodynamic equilibrium. Kinetic data indicate that esters form when carboxylic acid traps rapidly isomerizing carbenium ions on the catalyst’s surface. Competition is fierce for esterification sites among olefins, carboxylic acid, and esters, and olefins occupy few esterification sites. Contrastingly, olefins triumph in competition for isomerization sites, and olefin isomerization is much faster than esterification. Heptanoic acid exists primarily in dimer form, but the monomer form reacts to make esters. A complex kinetic model fit experimental data for double bond isomerization, conversion of olefin to esters, and the distribution of secondary esters that formed over 22 h.

Effect of n-butanol cofeeding on the deactivation of methanol to olefin conversion over high-silica HZSM-5: A mechanism and kinetic study

The co-reaction of methanol and n-butanol that instantaneously dehydrated into 1-butene at the inlet was performed to evaluate the effect of co-feeding olefin on the catalyst deactivation from coke deposition over HZSM-5 with Si/Al = 200 at 460 °C, a practical situation encountered by commercial methanol to propylene (MTP) process. It was revealed that the deactivation was an autocatalytic process depending on both methanol and products. In particular, increasing inlet methanol fraction would dramatically accelerate activity attenuation, and the co-feeding butanol significantly reduces activity loss by promoting methanol conversion. The deactivation is generally non-selective to methanol transformation and product generation, except for methane. A possible deactivation mechanism was proposed with the coke precursor originated from the methylation of lower polymethylbenzenes to higher tardy ones. A deactivation kinetic model was then developed, which gave fairly good prediction to the experimental results in a wide range of feed composition.

Current State of the Art of the Solid Rh-Based Catalyzed Hydroformylation of Short-Chain Olefins

The hydroformylation of olefins is one of the most important homogeneously catalyzed processes in industry to produce bulk chemicals. Despite the high catalytic activities and selectivity’s using rhodium-based homogeneous hydroformylation catalysts, catalyst recovery and recycling from the reaction mixture remain a challenging topic on a process level. Therefore, technical solutions involving alternate approaches with heterogeneous catalysts for the conversion of olefins into aldehydes have been considered and research activities have addressed the synthesis and development of heterogeneous rhodium-based hydroformylation catalysts. Different strategies were pursued by different groups of authors, such as the deposition of molecular rhodium complexes, metallic rhodium nanoparticles and single-atom catalysts on a solid support as well as rhodium complexes present in supported liquids. An overview of the recent developments made in the area of the heterogenization of homogeneous rhodium catalysts and their application in the hydroformylation of short-chain olefins is given. A special focus is laid on the mechanistic understanding of the heterogeneously catalyzed reactions at a molecular level in order to provide a guide for the future design of rhodium-based heterogeneous hydroformylation catalysts.

Catalytic Longevity of Hierarchical SAPO-34/AlMCM-41 Nanocomposite Molecular Sieve In Methanol-to-Olefins Process.

SAPO-34/AlMCM-41, as a hierarchical nanocomposite molecular sieve was prepared by sequential hydrothermal and dry-gel methods studied for catalytic conversion of methanol to light olefins. Pure AlMCM-41, SAPO-34, and their physical mixture were also produced and catalytically compared. Physicochemical properties of materials were mainly investigated using XRD, N2 isothermal adsorption-desorption, FESEM, FT-IR, NH3-TPD, and TG/DTG/DTA techniques. Micro-meso hierarchy of prepared composite was demonstrated by XRD and BET analyses. Catalytic performance of materials illustrated that the methanol conversion of the prepared composite was about 98% for 120 min, showing a higher activity than the other catalysts. The initial reaction selectivity to light olefins of the composite was also comparable with those for the other catalysts. Furthermore, the results revealed that SAPO-34/AlMCM-41 preparation decreased the concentration and strength of active acid sites of the catalyst which could beneficially affect the deposition of heavy molecular products on the catalyst. However, as observed, the prepared composite was deactivated in olefins production faster than pure SAPO-34. The small mean pore diameter of composite could be mainly responsible for its pore blockage and higher deactivation rate. Meanwhile, since the SAPO-34 prepared by dry-gel method had inherently high mesoporosity, the AlMCM-41 introduction did not promote the molecular diffusion in the composite structure. The coke content was found 15.5% for deactivated composite smaller than that for the SAPO- 34 catalyst which could be due to the pore blockage and deactivation of the composite in a shorter period.

Low-Temperature Methane Oxidation Triggered by Peroxide Radicals over Noble-Metal-Free MgO Catalyst.

Methane is a greenhouse gas that contributes to global warming. Hence, effectively removing the low concentration (<1000 ppm) of methane in the environment is an issue that deserves research in the field of catalysis. In this study, oxygen-magnesium bivacancies are simultaneously imbedded into MgO by designing an in situ reduction combustion atmosphere for oxygen release and substituting magnesium with carbon to induce the formation of magnesium vacancies. The DFT calculations reveal that the surface electron density of MgO is improved by the oxygen vacancy structure and the substitution of Mg by C in bulk; this accelerates migration of the charge from the material surface to the adsorbed oxygen species, which leads to abundant surface peroxide species that enable activation and oxidation of methane at a low temperature (below 200 °C). This work could provide a concept for developing non-noble or transition metal oxides for low-temperature activation and conversion of alkanes in the thermocatalytic field through reactive oxygen species.

Role of Texture and Acidity of SAPO-34 in Methanol to Olefins Conversion

The effect of the amount of the molecular template tetraethylammonium hydroxide (TEAOH) in the precursor mixture on the physicochemical properties of SAPO-34 crystals has been examined, and the catalysts obtained have been tested in methanol conversion to lower olefins (MTO). The analysis of the textural and acidic properties of SAPO-34, which determine the high catalytic performances of catalysts in MTO, has been carried out. An effective catalyst possesses a high acidity and a developed surface with a large specific mesopore volume.

Selective generation of aromatic hydrocarbons from hydrotreating-cracking of bio-oil light fraction with MOx modified HZSM-5 (M = Ga, Mo and Zn)

The upgrading of highly unsaturated bio-oil by zeolite cracking suffers from severe catalyst deactivation due to the carbonaceous deposition. Therefore, the dual-stage hydrotreating-cracking process is developed for more stable operation. In this work, to further promote the generation of aromatic hydrocarbon in a hydrotreating-cracking process cofeeding bio-oil light fraction and methanol, the cracking catalyst HZSM-5 was modified by MOx (M = Ga, Mo and Zn). Compared with the blank HZSM-5, the promotion of aromatic hydrocarbon production by MoO3/HZSM-5 was mainly owing to the enhanced selective conversion of intermediate light alkenes to aromatics, while those by Ga2O3/HZSM-5 and ZnO/HZSM-5 were attributed to both the re-activation of hydrotreating-derived CH4 and the intensified selective aromatization of alkenes. Meanwhile, raising cracking temperature decreased the yield of aromatic hydrocarbon but favored the production of gases. Ga2O3/HZSM-5 was the most effective catalyst for aromatic hydrocarbon production and 400 °C was a suitable cracking temperature, under which the upgrading of a bio-oil aqueous fraction achieved the oil phase yield of above 22% with the aromatic hydrocarbon content of above 93%.

Effect of coating with silica on acidic and catalytic properties of SAPO-18 in MTO conversion

Abstract Silicoaluminophosphate with AEI structure has been modified by silica coating using polydimethylsiloxane (PDMS) and tetraethoxysilane (TEOS) as silica sources. The single step procedure including deposition of 0.5, 1.0, 1.5 and 2.0 wt% of silicon in one step and the multistep procedure including stepwise deposition of silica source by small portions corresponding to 0.5 wt% of silicon with intermediate calcination steps have been applied. The modified materials have been characterized by X-ray fluorescence spectroscopy, X-ray diffraction analysis, low temperature nitrogen adsorption, 29Si MAS NMR, thermoprogrammed desorption of ammonia and FTIR spectroscopy of adsorbed 2,6-ditertbutylpyridine (2,6-DTBPy). The results show that multistep procedure leads to the gradual increase of silicon content and results in the deposition of 2 wt% of Si in 4 steps, whereas single step procedure does not lead to the desired result. Coating with silicon leads to poisoning of Bronsted acid sites located on the external surface of SAPO-18 crystal. This effect is more pronounced in the case of PDMS due to more uniform silica deposition in this case. Coated materials show higher stability of catalytic activity with time on stream in methanol to olefins conversion (MTO) and higher selectivity to light olefins. The mechanism of silica coating with PDMS and TEOS is discussed.

Kinetics of low-temperature methane activation on IrO2(1 1 0): Role of local surface hydroxide species

The ability of the IrO2(1 1 0) surface to promote CH4 activation at low temperatures (~150 K) suggests possibilities for developing IrO2-based catalysts to selectively convert light alkanes to high-value chemicals. In this study, we present experimental results and microkinetic simulations, based on density functional theory (DFT) calculations, of temperature programmed reaction spectra (TPRS) obtained for CH4 σ-complexes adsorbed on IrO2(1 1 0), and focus on clarifying how surface OH groups modify the branching between CH4 desorption, activation and subsequent reactions during TPRS. Our DFT results predict that surface OH groups strongly destabilize CH4 σ-complexes on IrO2(1 1 0) in addition to deactivating surface O-atoms that are needed to achieve CH4 activation at low temperature. We demonstrate that a microkinetic model that incorporates the influence of surface OH groups on the CH4 binding and reactivity reproduces experimental TPRS results which show that adsorbed CH4 σ-complexes preferentially dissociate at low CH4 coverage, but that an increasing fraction of the adsorbed CH4 desorbs at low temperature (~120 K) with increasing initial CH4 or H coverage. The simulations reveal that low-temperature CH4 desorption during TPRS arises primarily from CH4 σ-complexes that are kinetically-trapped between adjacent surface OH groups, and are thus destabilized and unable to access reactive O-atoms. In addition, when the effect of adjacent OH groups is incorporated we find that the PBE-D3 functional incorporating dispersion provides CH4 binding energies that agree more closely with that obtained from the TPRS experiments. Our results demonstrate that the local effect of adjacent OH groups must be incorporated into any microkinetic models to properly capture the selectivity between extensive and partial oxidation in alkane conversion on IrO2(1 1 0) under reaction conditions.

Generation and Reactivity of 2-Amido-1,3-diaminoallyl Cations: Cyclic Guanidine Annulations via Net (3 + 2) and (4 + 3) Cycloadditions.

Toward a method for direct conversion of alkenes to cyclic guanidines, we report that 1,3-dipolar cycloadditions of 2-amido-1,3-diamino allylic cations with alkenes provide a new method for direct cyclic guanidine annulation. Generated under oxidative conditions, the 2-amido-1,3-diaminoallyl cations react as 1,3-dipoles providing rapid access to 2-amino imidazolines through net (3 + 2) cycloadditions. The utility is demonstrated through a concise synthesis of the oroidin alkaloid, phakellin. The described 1,3-dipole also participates in net (4 + 3) cycloadditions with dienes.

Spatially Ordered Arrangement of Multifunctional Sites at Molecule Level in a Single Catalyst for Tandem Synthesis of Cyclic Carbonates.

With fossil energy resources increasingly drying up and gradually causing serious environmental impacts, pursuing a tandem and green synthetic route for a complex and high-value-added compound by using low-cost raw materials has attracted considerable attention. In this regard, the selective and efficient conversion of light olefins with CO2 into high-value-added organic cyclic carbonates (OCCs) is of great significance owing to their high atom economy and absence of the isolation of intermediates. To fulfill this expectation, a multifunctional catalytic system with controllable spatial arrangement of varied catalytic sites and stable texture, in particular, within a single catalyst, is generally needed. Here, by using a stepwise electrostatic interaction strategy, imidazolium-based ILs and Au nanoparticles (NPs) were stepwise immobilized into a sulfonic group grafted MOF to construct a multifunctional single catalyst with a highly ordered arrangement of catalytic sites. The Au NPs and imidazolium cation are separately responsible for the selective epoxidation and cycloaddition reaction. The mesoporous cage within the MOF enriches the substrate molecules and provides a confined catalytic room for the tandem catalysis. More importantly, the highly ordered arrangement of the varied active sites and strong electrostatic attraction interaction result in the intimate contact and effective mass transfer between the catalytic sites, which allow for the highly efficient (>74% yield) and stable (repeatedly usage for at least 8 times) catalytic transformation. The stepwise electrostatic interaction strategy herein provides an absolutely new approach in fabricating the controllable multifunctional catalysts, especially for tandem catalysis.

Efficient and selective ethane-to-ethylene conversion assisted by a mixed proton and electron conducting membrane

Direct conversion of alkanes into valuable chemicals has attracted significant interest in recent decades by academia and industry alike due to the vast economic potential. One type of such conversions is non-oxidative dehydrogenation (NODH), which is deemed advantageous over its oxidative counterpart in conversion and selectivity. However, coking-related degradation is a major challenge to the NODH route. We here demonstrate an efficient and selective ethane-to-ethylene conversion membrane reactor operating on NODH and a mixed electron and proton conductor (MEPC) having a composition of BaCo0.4Fe0.4Zr0.1Y0.1O3 (BCFZY). The H2 produced from NODH is instantly removed by BCFZY, thus shifting the equilibrium to maximize conversion and selectivity. The results show that the single-pass ethane-to-ethylene conversion, ethylene selectivity and product yield at 700 °C are 70, 90 and 63%, respectively, with a moistened ethane as the feedstock. During a 100-h durability testing, there is virtually no degradation observed in membrane performance.

Ni/MgO Catalysts on Structured Metal Supports for the Air Conversion of Low Alkanes into Synthesis Gas

Ni/MgO Catalysts on Structured Metal Supports for the Air Conversion of Low Alkanes into Synthesis Gas

Preparing MoVTeNbBiO Catalysts for the Selective Oxidative Conversion of Light Alkanes

Preparing MoVTeNbBiO Catalysts for the Selective Oxidative Conversion of Light Alkanes

Probing the active sites for methane activation on Ga/ZSM-5 zeolites with solid-state NMR spectroscopy.

Ga-modified zeolites represent the most effective catalyst for catalytic transformation of light alkanes to aromatics. GaO+ ions and GaOx clusters on Ga/ZSM-5 zeolites are probed by solid-state NMR. These two types of Ga species show strong Lewis acidity and are quantitatively correlated with the catalytic activity of Ga/ZSM-5 for methane C-H bond activation. The interaction between the surface Ga species and zeolite is characterized by using double-resonance solid-state NMR spectroscopy, which provides direct spectroscopic evidence for the location and distribution of active Ga species. These results provide new insight into the understanding of the nature and role of Ga species in Ga-modified zeolites for the conversion of light alkanes.

Non-thermal plasma induced photocatalytic conversion of light alkanes into high value-added liquid chemicals under near ambient conditions.

We reported a novel non-thermal plasma induced photocatalytic transformation of light hydrocarbons over Ti-Ga/UZSM-5, which gives 47.8 C% of liquid products, with C6-C9 iso-alkanes being the major components, and limited coke (5.5 C%). Combining the plasma with a photocatalyst displays great potential to produce gasoline range chemicals from low-cost gaseous hydrocarbons under near ambient conditions.

Oxidative steam conversion of light alkanes

Oxidative steam reforming of C2-C4 alkanes was studied in an annular catalytic reactor under atmospheric pressure over two catalysts. Concentrations of the products of chemical reactions in the outlet gas mixture were measured at different temperatures of reactor. Effects of temperature have been compared for different residence time for the inlet gas ratio water/air/C2-C4 alcanes of 7: 4.5:1.

Structure, Dynamics, and Reactivity for Light Alkane Oxidation of Fe(II) Sites Situated in the Nodes of a Metal-Organic Framework.

Metal organic frameworks (MOFs), with their crystalline, porous structures, can be synthesized to incorporate a wide range of catalytically active metals in tailored surroundings. These materials have potential as catalysts for conversion of light alkanes, feedstocks available in large quantities from shale gas that are changing the economics of manufacturing commodity chemicals. Mononuclear high-spin (S = 2) Fe(II) sites situated in the nodes of the MOF MIL-100(Fe) convert propane via dehydrogenation, hydroxylation, and overoxidation pathways in reactions with the atomic oxidant N2O. Pair distribution function analysis, N2 adsorption isotherms, X-ray diffraction patterns, and infrared and Raman spectra confirm the single-phase crystallinity and stability of MIL-100(Fe) under reaction conditions (523 K in vacuo, 378-408 K C3H8 + N2O). Density functional theory (DFT) calculations illustrate a reaction mechanism for the formation of 2-propanol, propylene, and 1-propanol involving the oxidation of Fe(II) to Fe(III) via a high-spin Fe(IV)═O intermediate. The speciation of Fe(II) and Fe(III) in the nodes and their dynamic interchange was characterized by in situ X-ray absorption spectroscopy and ex situ Mössbauer spectroscopy. The catalytic relevance of Fe(II) sites and the number of such sites were determined using in situ chemical titrations with NO. N2 and C3H6 production rates were found to be first-order in N2O partial pressure and zero-order in C3H8 partial pressure, consistent with DFT calculations that predict the reaction of Fe(II) with N2O to be rate determining. DFT calculations using a broken symmetry method show that Fe-trimer nodes affecting reaction contain antiferromagnetically coupled iron species, andhighlight the importance of stabilizing high-spin (S = 2) Fe(II) species for effecting alkane oxidation at low temperatures (<408 K).