Propene Metathesis Research Articles

Enhancement of Propylene Metathesis Performance of MoO3/Al2O3 with Promotion of Phosphoric Acid

AbstractCatalytic olefin metathesis represents a vital reaction in the chemical industry, as it provides a feasible route for the interconversion of olefins. However, traditional supported catalysts usually suffer from low activity due to sluggish kinetics for the formation of catalytically active metal‐carbene species. This work tackles this issue by taking phosphoric acid as a promoter and constructing a Brønsted acidic site to cooperate with the MoOx sites, thus facilitating the formation of Mo‐carbene. It turns out that the turnover frequency of propene metathesis over the Mo−P/Al2O3 catalyst is 7.1 times higher than that over the unmodified Mo/Al2O3 catalyst. The combined characterization reveals the promotion of phosphorus results from the alignment of olefin toward adjacent MoOx and thus facilitates formation of active Mo‐carbene species.

Propylene Metathesis over Molybdenum Silicate Microspheres with Dispersed Active Sites.

In this work, we demonstrate that amorphous and porous molybdenum silicate microspheres are highly active catalysts for heterogeneous propylene metathesis. Homogeneous molybdenum silicate microspheres and aluminum-doped molybdenum silicate microspheres were synthesized via a nonaqueous condensation of a hybrid molybdenum biphenyldicarboxylate-based precursor solution with (3-aminopropyl)triethoxysilane. The as-prepared hybrid metallosilicate products were calcined at 500 °C to obtain amorphous and porous molybdenum silicate and aluminum-doped molybdenum silicate microspheres with highly dispersed molybdate species inserted into the silicate matrix. These catalysts contain mainly highly dispersed MoOx species, which possess high catalytic activity in heterogeneous propylene metathesis to ethylene and butene. Compared to conventional silica-supported MoOx catalysts prepared via incipient wetness impregnation (MoIWI), the microspheres with low Mo content (1.5-3.6 wt %) exhibited nearly 2 orders of magnitude higher steady-state propylene metathesis rates at 200 °C, approaching site time yields of 0.11 s-1.

Mechanistic study of heterogeneous propene metathesis on WOx/SiO2 catalysts

Silica-supported tungsten oxides are widely used industrial catalysts for olefin metathesis due to their low cost and robustness, yet the mechanisms for heterogeneously catalyzed metathesis reactions remain comparatively less understood. In this work, density-functional theory (DFT) calculations were used to study the model reactions of propene metathesis. Our calculations confirm that the metathesis reactions catalyzed by WOx/SiO2 largely follow the Chauvin cycle, with an overall energetic barrier of 142 kJ/mol. To understand how the initial alkylidene active sites are generated, three mechanisms were examined: The pseudo-Wittig mechanism was found to be most favorable and proceeds with a metallacycle intermediate, while the allylic and vinylic CH activations are much more difficult and require the reduction of surface sites to W(+4). Relative to the adsorbed reactant state, the overall intrinsic barriers for three mechanisms were computed to be 193, 261, and 355 kJ/mol, respectively. The higher barriers for active-site formation than for the metathesis cycle are consistent with the difficult, high-temperature pretreatment required in experiments to activate WOx/SiO2 catalysts.

Solid-Phase Synthesis of Nickel–Molybdenum Catalysts for Propylene Metathesis under Mechanical Activation

Solid-Phase Synthesis of Nickel–Molybdenum Catalysts for Propylene Metathesis under Mechanical Activation

Promoting active site renewal in heterogeneous olefin metathesis catalysts.

As an atom-efficient strategy for the large-scale interconversion of olefins, heterogeneously catalysed olefin metathesis sees commercial applications in the petrochemical, polymer and speciality chemical industries1. Notably, the thermoneutral and highly selective cross-metathesis of ethylene and 2-butenes1 offers an appealing route for the on-purpose production of propylene to address the C3 shortfall caused by using shale gas as a feedstock in steam crackers2,3. However, key mechanistic details have remained ambiguous for decades, hindering process development and adversely affecting economic viability4 relative to other propylene production technologies2,5. Here, from rigorous kinetic measurements and spectroscopic studies of propylene metathesis over model and industrial WOx/SiO2 catalysts, we identify a hitherto unknown dynamic site renewal and decay cycle, mediated by proton transfers involving proximal Brønsted acidic OH groups, which operates concurrently with the classical Chauvin cycle. We show how this cycle can be manipulated using small quantities of promoter olefins to drastically increase steady-state propylene metathesis rates by up to 30-fold at 250 °C with negligible promoter consumption. The increase in activity and considerable reduction of operating temperature requirements were also observed on MoOx/SiO2 catalysts, showing that this strategy is possibly applicable to other reactions and can address major roadblocks associated with industrial metathesis processes.

Ethylene Maximization with Propylene Metathesis

Ethylene Maximization with Propylene Metathesis

Effect of Support Treatment with Modifiers, (NH4)2SiF6 and H3BO3, on the Catalytic Properties of Mo/Al2O3 in Propylene Metathesis

Effect of Support Treatment with Modifiers, (NH4)2SiF6 and H3BO3, on the Catalytic Properties of Mo/Al2O3 in Propylene Metathesis

Propane metathesis and hydrogenolysis over titanium hydride catalysts

Propane metathesis reactions over group 2–5 metal hydrides were investigated where TiH2 exhibited the highest butane formation amount. This study is the first example of carbon–carbon bond cleavage and formation over bulk metal hydrides.

Olefin metathesis over supported MoOx catalysts: influence of the oxide support

Supported MoOx catalysts on oxide supports (Al2O3, TiO2, ZrO2, SiO2) were synthesized for propylene metathesis, characterized with in situ spectroscopies (DRIFTS, Raman, UV-vis) and chemically probed with propylene-TPSR, ethylene/2-butene titration.

Влияние фторирования катализатора MoO3/Al2O3 на протекание метатезиса пропилена

In the course of this work, fluorinated catalysts MoO3/Al2O3-F for the olefins metathesis have been synthesized. The materials have been characterized by various physicochemical methods and tested in the propylene metathesis reaction. It has been shown that the support fluorination leads to partial replacement of surface hydroxyl groups by F, which is accompanied by an increase in the strength of both Lewis acid sites and residual bridging OH groups. Increasing the fluorine content on γ-Al2O3 up to 3 wt. % leads to an increase in the conversion of propylene in the metathesis reaction by 1.5 times (WHSV = 1.1 h-1, Т = 100 °С, р = 9 atm.) with a selectivity of more than 95%. However, when the reaction is carried out at atmospheric pressure, fluorinated samples show lower activity than unpromoted ones. The results of this work show that the support acidity plays an important role in propylene metathesis. The proposed method of catalyst modification opens up new possibilities for improving classical metathesis catalysts.

Solid-Phase Synthesis of Nickel-Molybdenum Catalysts for Metathesis of Propylene under Mechanical Action

The solid-phase synthesis of model aluminum-molybdenum (Al-Mo) and aluminum-nickel-molybdenum (Al-Ni-Mo) compositions constituting the catalysts for metathesis of propylene was carried out under mechanical action. The structure of model Al-Mo and Al-Ni-Mo compositions was studied using X-ray diffraction analysis, high-resolution transmission electron microscopy, infrared spectroscopy, and diffuse reflectance electron spectroscopy (UV-vis DRS). The latter method revealed the presence of isolated monomeric and oligomeric molybdate compounds in the model Al-Ni-Mo compositions. Granulated catalysts for metathesis were obtained by molding the model Al-Mo and Al-Ni-Mo compositions with aluminum hydroxide followed by calcination. Most active in the metathesis of propylene was the aluminum-molybdenum catalyst containing 2.6 wt.% Ni, 13.0 wt.% Mo and 32.7 wt.% Al. At the process temperature of 200 °С, pressure 0.1 MPa, and weight space velocity of propylene 1 h–1, the conversion of propylene on this catalyst reached 33.7 %, which makes the catalyst promising for practical application. Therewith, the weight fraction of ethylene in the reaction products was 17.5 %, and butenes – 71.3 %.

Promoting effect of MoO3/Al2O3 catalysts fluorination on their reactivity in propylene metathesis

Supported MoO3/Al2O3-F catalysts were synthesized and characterized by Raman, IR, and NMR spectroscopy. It was shown that support fluorination leads to partial substitution of surface OH groups with F which is accompanied by increases the strength of both LAS (Lewis Acid Sites) and residual bridging OH groups. But the change in the acidity doesn’t affect the structure of surface molybdenum forms. An increase of the fluorine content on γ-Al2O3 up to 6 wt% leads to 4.7-fold increase of the propylene conversion in metathesis reaction (WHSV = 11 h−1, T = 100 °C, p = 9 atm.) with selectivity above 95 %. The results prove that the support acidity plays an important role in the propylene metathesis. The catalyst modification method proposed here opens new opportunities for the improvement of classical metathesis catalysts.

Tuning the metathesis performance of a molybdenum oxide-based catalyst by silica support acidity modulation and high temperature pretreatment

Al-Doping of the mesoporous silica support and pre-treatment of the molybdenum oxide-based catalyst in a stream of hydrocarbons or carbon monoxide at high temperature increase significantly its catalytic performance in propylene metathesis.

Activity Trends in the Propane Dehydrogenation Reaction Catalyzed by MIII Sites on an Amorphous SiO2 Model: A Theoretical Perspective

One class of particularly active catalysts for the Propane Dehydrogenation (PDH) reaction are well-defined M(III) sites on amorphous SiO2. In the present work, we focus on evaluating the catalytic trends of the PDH for four M(III) single-sites (Cr, Mo, Ga and In) on a realistic amorphous model of SiO2 using density functional theory-based calculations and the energetic span model. We considered a catalytic pathway spanned by three reaction steps taking place on selected MIII–O pair of the SiO2 model: σ-bond metathesis of propane on a MIII–O bond to form M-propyl and O–H group, a β-H transfer step forming M–H and propene, and the H–H coupling step producing H2 and regenerating the initial M–O bond. With the application of the energetic span model, we found that the calculated catalytic activity for Ga and Cr is comparable to the ones reported at the experimental level, enabling us to benchmark the model and the methodology used. Furthermore, results suggest that both In(III) and Mo(III) on SiO2 are potential active catalysts for PDH, provided they can be synthesized and are stable under PDH reaction conditions.

Identifying the Catalytic Active Site for Propylene Metathesis by Supported ReOx Catalysts

A series of supported ReOx catalysts were investigated that allowed identifying the unique surface anchoring sites on oxide supports responsible for activating the surface ReO4 sites for propylene ...

Propane to olefins tandem catalysis: a selective route towards light olefins production.

On-purpose synthetic routes for propylene production have emerged in the last couple of decades in response to the increasing demand for plastics and a shift to shale gas feedstocks for ethylene production. Propane dehydrogenation (PDH), an efficient and selective route to produce propylene, saw booming investments to fill the so-called propylene gap. In the coming years, however, a fluctuating light olefins market will call for flexibility in end-product of PDH plants. This can be achieved by combining PDH with propylene metathesis in a single step, propane to olefins (PTO), which allows production of mixtures of propylene, ethylene and butenes, which are important chemical building blocks for a.o. thermoplastics. The metathesis technology introduced by Phillips in the 1960s and mostly operated in reverse to produce propylene, is thus undergoing a renaissance of scientific and technological interest in the context of the PTO reaction. In this review, we will describe the state-of-the-art of PDH, propylene metathesis and PTO reactions, highlighting the open challenges and opportunities in the field. While the separate PDH and metathesis reactions have been extensively studied in the literature, understanding the whole PTO tandem-catalysis system will require new efforts in theoretical modelling and operando spectroscopy experiments, to gain mechanistic insights into the combined reactions and finally improve catalytic selectivity and stability for on-purpose olefins production.

Design of hybrid pellet catalysts of WO3/Si-Al and PtIn/hydrotalcite via dehydrogenation and metathesis reactions for production of olefins from propane

The design of hybrid pellet catalysts for dehydrogenation and metathesis of propane to olefins was investigated. Reaction kinetics and mathematical models of pellet catalysts in a reactor were developed and simulated using gPROMS. Three types of pellet catalysts including uniformly mixed, dehydrogenation-core (MDM) and dehydrogenation-shell (DMD) were compared with physically mixed pellet catalysts. A sensitivity analysis of operating conditions, ratios, types and sizes of pellet catalysts were performed to determine the optimal parameters offering a maximum alkene yield. The most suitable pellet catalyst type was DMD. Depending on operating conditions, the optimal DMD had a core metathesis diameter of between 0.28 and 3.43 mm, with spherical particles between 1 and 7 mm in diameter. The optimal DMD showed increased alkene yield up to 43%, while alkene selectivity improved by 25–35% from the base case. The amount of dehydrogenation catalysts reduced from the base case by approximately 59%.

Differences in acid and catalytic properties of W incorporated spherical SiO2 and 1%Al-doped SiO2 in propene metathesis

Propene self-metathesis to ethylene and 2-butene was investigated over tungsten-based catalysts (9 wt.% W) supported on silica and 1%Al-doped SiO2, prepared by different processes. On pure SiO2, incorporating WOx improved tungsten dispersion and formation of active tetrahedral WOx species, compared to the impregnated ones. However, negative effect was found when tungsten was incorporated in the 1%Al-doped SiO2 as the catalysts contained more crystalline WOx, lower tetrahedral species, and lower Lewis acid sites, compared to the W-imp 1Al2O3/SiO2 prepared by impregnation. Incorporating both W and Al in the SiO2 by sol-gel method may lead to suppression of bridge hydroxyl Si(OH)Al group, as a consequence more crystalline WOx was formed. Nevertheless, the abundance of Bronsted and Lewis acid was found to play important role in the propene metathesis and the secondary metathesis of 1-butene reactions than surface silanol and the presence of tetrahedral tungsten oxide species on the 1%Al-doped SiO2 supported catalysts.

Preferential formation of 1-butene as a precursor of 2-butene in the induction period of ethene homologation reaction on reduced MoO3/SiO2 catalyst

Ethene homologation reaction to give propene (3C2H4 → 2C3H6) was examined on reduced molybdena silica (MoO3/SiO2) catalyst at initial ethene pressure around 14.66 kPa (110 mmHg) and a temperature of 30 °C. In the very first stage of the ethene homologation reaction, induction period was observed as well as previous results reported in the references. During the induction period, ethene dimerization providing 1-butene was preferentially occurred. In addition, it was indicated that isomerization of 1-butene to 2-butene was retarded by the presence of excess ethene as a raw material. Therefore, it might be considered that the induction period of the ethene homologation reaction on the reduced MoO3/SiO2 catalyst might be caused by insufficiency of 2-butene to promote reverse propene metathesis (CH2=CH2+CH3-CH=CH-CH3 → 2CH2=CH-CH3).

Formation of isolated tungstate sites on hierarchical structured SiO2- and HY zeolite-supported WOx catalysts for propene metathesis

The formation of isolated tungstate sites on hierarchical structured SiO2 nanoparticles and HY zeolite with high Si/Al ratio (Si/Al 500) was investigated in the self-metathesis of propene over supported WOx-based catalysts. The synthesis of hierarchical HY not only increased the tungsten dispersion in the forms of isolated tungstate oxo species (mono-oxo and di-oxo) by increasing the terminal silanol group density of the support for these oxides to be grafted on but also greatly reduced the heavy hydrocarbon formation simultaneously by elimination of some alumina from the zeolite. As a consequence, higher propene conversion was obtained without the undesired reactions especially during the initial stage, when the metallocarbene was not fully developed. The results present a facile method for the development of heterogeneous WOx-based metathesis catalysts and a better correlation between the surface properties of catalyst support and the formation of tungsten pre-catalysis active species.