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The distribution of titanium (Ti) active sites in the framework of TS-1 zeolite is one of the critical factors affecting its catalytic performance, since it can influence accessibility of the Ti active sites and the catalytic utilization of Ti atoms. Here, TS-1 zeolite with homogeneous distribution of titanium atoms in the framework (named BUS-TS-1) is successfully synthesized via bottom-up strategy at high basicity conditions, and BUS-TS-1 zeolite exhibits better catalytic performance for both olefin and alkane oxidation. The comprehensive explorations on the crystallization behavior of BUS-TS-1 zeolite show that, the gripper-like silicon species, as condensed matter in Q2 and Q3 states (detected by 29Si NMR), can be obtained by the condensation of tetraethyl orthosilicate (TEOS) at high alkalinity conditions. The gripper-like silicon species can condense with Ti-OH to form stable and isolated Si-O-Ti species, so that the phase transfer rates of Si and Ti species match during the entire crystallization process, resulting in the homogeneous distribution of Ti atoms. This work offers a useful strategy for the synthesis of high-performance catalysts by regulating the distribution of Ti active-site within TS-1 framework.

fff; International audience; Polymeric carbon was deposited over Siralox supported cobalt catalysts by an ethylene treatment at 230 °C and 260 °C. Cobalt catalysts with cobalt particle sizes of 10 and 14 nm were studied. Temperature programmed hydrogenation and Raman spectroscopy analyses of the deposited species were found to be similar to those formed during Fischer-Tropsch synthesis. The cobalt catalysts were tested in high-throughput 16 parallel reactors at 20 bars and 220 °C, using a H2/CO ratio of 2.12. Data were collected at different space times to compare activities and selectivities at iso-conversion levels. Ethylene treated catalysts showed lower activity that corresponded roughly to the loss of CO adsorption sites. Additionally, a decrease of the heavy products selectivity, an increase in the methane selectivity and a decrease of the olefin to paraffin ratio was observed after the ethylene treatments. Unlike the loss in activity, the deselectivation level was found to depend on the amount of deposited carbon. This phenomenon can be explained by a steric effect of the deposit, but an electronic effect cannot be excluded, but is challenging to prove.

Facile strategies for noble metal dispersion in the shell-layer of core–shell structured metal–organic frameworks based on Zr-MOFs (UiO-66@Pd-UiO-67-BPY) was developed. The robust structure of the core-structure UiO-66 was firstly synthesized before covering up with a shell-structure of UiO-67-BPY obtaining the core–shell structure (UiO-66@UiO-67-BPY). The metallation with active palladium species (PdII) was designed on the shell-layer of core–shell MOFs via a post-synthetic method. The Pd species were coordinated explicitly in a bidentate manner to the bipyridyl linkers of the shell-structure (UiO-67-BPY). Excellent dispersion of Pd in the shell structure was obtained, resulting in UiO-66@Pd-UiO-67-BPY, as confirmed from characterizations. Taking advantage of the designed catalyst, the synthesized UiO-66@Pd-UiO-67-BPY was examined for the catalytic hydrogenation reaction. The results revealed an excellent catalytic performance of UiO-66@Pd-UiO-67-BPY compared with the traditional catalyst Pd-UiO-67-BPY. Moreover, the designed catalyst structure exhibited outstanding performance and paved the way towards a cost-effective catalyst synthesis based on MOFs combined with a noble metal.

Indium-based oxides are potential catalysts for CO2 hydrogenation to methanol. However, upon complexing with SAPO-34, they give a C2=–C4= yield below 7.3% due to production of large amounts of CO and CH4 at high CO2 conversion. Therefore, a large improvement of the C2=–C4= yield over indium-based oxide and zeolite composites is a challenge. In this context, InCeOx and InCrOx oxides were prepared and found to produce more methanol than In2O3 or In–Zr oxide. Experimental and DFT calculation results reveal that incorporation of Ce or Cr into In2O3 generates more surface oxygen vacancies and enhances the electronic interaction between HCOO* intermediates and the catalyst surface, which decreases HCOO* and CH3OH formation free energy barriers and enthalpy barriers. Compared with InCeOx(0.13) and In2O3, InCrOx(0.13) shows higher catalytic activity for CO2 hydrogenation, and by coupling with SAPO-34, it gives a C2=–C4= yield of 1.5–2.0 times those obtained on In2O3/SAPO-34 and In-Zr/SAPO-34 at CO2 conversion of 33.6%.

Two sets of bio-inspired non-heme iron complexes, each comprising of an FeII and FeIII species, bearing 16-membered macrocyclic tetradentate N-heterocyclic carbene ligands are reported. The complexes exhibit trans labile coordination sites, are characterized by means of NMR, ESI-MS, elemental analysis, SC-XRD and cyclic voltammetry and assessed as olefin epoxidation (pre-)catalysts applying H2O2 as oxidant. Sc(OTf)3 and AcOH are evaluated as Lewis and Bronsted acidic additives, respectively, resulting in partially noticeable improvement in catalytic performance. Hereby, complex 2b shows high stability (TON = 1000 at 20 °C), high temperature tolerance and advances in the more challenging epoxidation of terminal and functionalized olefins. Furthermore, in-depth DFT calculations are conducted to put the catalysts’ structural and electronic features into relation with the catalytic results.

This study unravels the effect of Mn promoter on the surface enrichment and competition of promoters and the evolutions of the chemical and structural of Fe species during the reaction, and illustrates the regulation of FeMn and FexCy for CO2 conversion and hydrogenation of intermediates. With the contents of Mn promoter increasing from 0.5% to 10.0%, the selectivity of light olefins decreasing from 38.73% to 30.58% and the ratio of olefin to paraffin decreases from 4.97 to 3.56. The surface ratio of Mn/Fe and Na/Fe is much higher than the impregnation ratio, which confirms the surface enrichment of Mn and Na promoters. It turns out that the iron oxides are transformed into iron carbides in the bulks and oligomeric FexOy on the surface after reaction. The enrichment of Mn promoters leads to more surface Fe species near the Mn promoters for the strong adsorption of CO2 and decreases the surface actual density of FexCy sites for the hydrogenation of CO to hydrocarbons, which consequently decreases the conversion of CO2 and the FTY value. The increasing content of Mn promoters from 0.5% to 3.0% also increases the adsorption ability of H2 on the surface of iron carbides, which is possibly associated with the hydrogenation of intermediates and leading to decreasing of the ratio of olefins to paraffins ranging from C2-C4.

Oxidative cracking, which combines catalytic oxidation and cracking reactions, represents a promising approach to reduce the energy and carbon intensities for light olefin production from naphtha. The need to co-feed gaseous oxygen with hydrocarbons, however, leads to significant COx formation and safety concerns. The cost and energy consumption associated with air separation also affects its economic attractiveness. In this study, we investigated a redox oxidative cracking (ROC) scheme and evaluated perovskites (La0.8Sr0.2FeO3 and CaMnO3) and Na2WO4-promoted perovskite (La0.8Sr0.2FeO3@Na2WO4 and CaMnO3@Na2WO4) as the redox catalysts for ROC. CaMnO3@Na2WO4 redox catalyst shows high activity, selectivity, and stability for light olefin production from cyclohexane. Operated under a redox oxidative cracking (ROC) scheme, CaMnO3@Na2WO4 enhances the catalytic cracking of cyclohexane, while showing high selectivity towards hydrogen combustion with its built-in, active lattice oxygen. Over three-fold increase in olefin yield compared to thermal cracking and 35% yield increase compared to conventional O2-cofeed oxidative cracking were achieved. Low energy ion scattering (LEIS), X-ray photoelectric spectroscopy (XPS), and differential scanning calorimetry (DSC) indicated a core-shell structure, where a molten Na2WO4 layer covers the CaMnO3 core. Na2WO4 modifies the oxygen donation behavior of CaMnO3 and provides a catalytically active surface for cyclohexane activation. In-situ XRD revealed that CaMnO3@Na2WO4 exhibited excellent structural stability and regenerability. The transformation of Mn4+ ↔ Mn3+ ↔ Mn2+ in CaMnO3, facilitated by reversible phase transition to (Ca/Mn)O solid solution, is responsible for the lattice oxygen donation and uptake during redox cycles. Electrochemical impedance spectroscopy (EIS) measurements further confirmed that the oxygen species were transported through the molten Na2WO4 layer to participate in ROC. These findings offer mechanistic insights to design effective redox catalysts for hydrocarbon valorization using the chemical looping strategy.

The one-pot tandem hydroformylation-reduction to synthesize alcohols from olefins is in great demand but suffering from low yields, poor selectivity and harsh condition. Herein, 1,10-phenanthroline (L1) modified Ir-catalyst proved to exhibit multiple catalysis in terms of FA dehydrogenation, hydroformylation of olefins, and transfer hydrogenation of aldehydes to accomplish the tandem hydroformylation-transfer hydrogenation of olefins with formic acid (FA) as hydrogen source, as the result of 52–70% yields for the target alcohols and the corresponding formate esters (obtained upon esterification of the alcohol with FA). In this sequence, only the use of FA with trans- and cis-conformers could fulfill the reduction of aldehydes to the alcohols through transfer hydrogenation as well as greatly depress hydrogenation of the olefin, which universally occurred in the high pressured gaseous H2. Both the in situ FT-IR spectroscopic analysis and the DFT-calculations verified that, over L1-[Ir(COD)Cl]2 catalyst, cis-FA serving as the hydride-ligand was responsible for the efficient dehydrogenation of FA to release H2 along with CO2, and trans-FA serving as the carbonyl O-containing ligand corresponded to the transfer hydrogenation of the aldehydes to the alcohols under the same catalytic conditions.

Late transition metal palladium catalysts chelated by benchmark α-diimine, phosphine-sulfonate, bisphosphine-monoxide ligands are of great interest for ethylene polymerization and challenging copolymerization with polar comonomers. Compared to numerous studies on the classic α-diimine and phosphine-sulfonate palladium catalysts, the new generation bisphosphine-monoxide palladium (BPMO-Pd) system is far less investigated. In this contribution, by skillfully designing a family of BPMO-Pd catalysts bearing differed steric and electronic P(III) phosphine groups, differed steric and electronic O = P(V) phosphine monoxide groups, and different connectivity of them, a comprehensive picture on catalyst structure construction is built for ethylene (co)polymerizations. This constructed catalyst structure-polymerization property relationship paves the way for the development of more efficient late transition metal catalysts for olefin (co)polymerization.

Two bio-inspired non-heme iron complexes bearing mixed tetradentate N-heterocyclic carbene/1,2,3-triazole ligands with cis labile coordination sites are reported. The compounds are studied in olefin epoxidation catalysis using H2O2 as oxidant. Sc(OTf)3, HClO4 and HOAc are applied as additives resulting in significant improvement of catalytic performance. Under optimized conditions the most active catalyst exhibits activities of 76,000 turnovers per hour, which is the highest reported value for an iron(II) catalyst. The complexes reveal comparably high stability and enable the challenging epoxidation of functionalized olefins. These results prove 1,2,3-triazoles to be promising and tunable ligands for iron catalyzed oxidation reactions.

A series of CrZn oxide catalysts with different Cr/Zn ratios were synthesized by co-precipitation and calcined at different temperatures. The catalysts were tested in a physical mixture with SAPO-34 in the direct conversion of syngas to olefins. X-ray diffraction, x-ray photoelectron and absorption spectroscopy, and electron microscopy were used to evaluate the impact of the Cr/Zn ratio and calcination temperature on the physicochemical properties of the resultant materials. CrZn–SAPO-34 catalysts were able to selectively convert syngas to C2–C3 hydrocarbons with a high olefin/paraffin ratio and low methane yield. However, the catalytic performance of these systems exhibited a trade-off between activity and stability in the olefin yield over time. By tuning the Cr/Zn ratio, it is possible to improve the olefin production stability, but with some compromise in the overall activity. The nonstoichiometric and inversed ZnCr2O4 spinel phase was considered to be the active phase for CO hydrogenation, while the decay in olefin production over time is correlated with abundance of ZnO on the resultant catalyst. Spectroscopic analysis demonstrated that the inversed spinel evolves toward its normal form under reaction conditions, which is accompanied by the formation of segregated ZnO; this phase may also increase the olefin hydrogenation activity. The challenge for the rational design of an optimal CrZn–SAPO-34 system is the stabilization of inversed ZnCr2O4, while minimizing the presence of the ZnO phase in the catalyst formulation.

The study was designed to investigate the catalytic hydrogenation of increasingly concerned CO2 to light olefins including ethylene, propylene and butylene, a series of critically important materials for various chemical syntheses, a win-win scenario for environment and economy. The Fe0.30Co0.15Zr0.30K0.10O1.63 catalyst, presented much poorer surface hydroxyl groups but richer oxygen vacancies (OVs) than the Fe0.60Co0.30K0.10O1.40, displayed light olefin space time yields (STY) of 4.93 mmol∙g-1cat∙h−1 at 310 °C and 2.0 MPa, which was 33.24% higher than the Fe0.60Co0.30K0.10O1.40 at the same reaction conditions. Extensive characterizations demonstrate that both oxygen vacancies (OVs) and surface hydroxyl groups ( OH) played important roles in the catalytic CO2 hydrogenation to light olefins, while OVs were more critical. OVs on the reduced Fe0.30Co0.15Zr0.45K0.10O1.63 were more active than those on the reduced Fe0.60Co0.30K0.10O1.40, which was very important to the enhancement of the oxygen storage, adsorption and activation of CO2 and thus the direct and efficient conversion of CO2 into CO, an important intermediate for the synthesis of light olefins synthesis. Thus, Fe0.30Co0.15Zr0.45K0.10O1.63 is a promising catalyst for converting CO2 hydrogenation to light olefins.

The organic products of the reaction between Cr(VI)/silica and ethylene, propene, 2-pentene, 1-hexene, or cyclohexene at temperatures between 25 and 150 °C were investigated to understand the formation of chromium sites active for polymerization. A wide assortment of products were obtained, either directly or through ligand displacement or extraction, which depended on the specific olefin and the conditions. Hydrocarbon products were released under conditions relevant to commercial operation and indicated both polymerization and acid catalysis: short olefin oligomers (from polymerization), alkanes (possibly from hydride transfer), internal olefins (from double bond shift) and isoalkylbenzenes (from skeletal isomerization and alkylation of the diluent benzene). Aldehydes, ketones, and alcohols were found in polar organic extraction media, some the result of aldol condensations in the extraction medium. Surface carboxylates, evident by in situ IR spectroscopy, could be detached from the catalyst only through hydrolysis. The high threshold to desorb oxygenates implies that the chromium sites retain self-generated ligands. The nature of these ligands depends on the reductant, and, consequently, the result may be an active or an inactive site. Consistently, reduction of Cr(VI)/silica by various olefins resulted in catalysts with different polymerization behavior, and addition of external ligands to Cr(II)/silica led to a poisoned or to an active catalyst, depending on the ligand.

Coke formation over MFI zeolites of different crystallite sizes was rigorously investigated in methanol-to-hydrocarbon conversion (MTH). The key experimental idea was based on the fact that soft coke in the zeolite micropores (internal coke) could be selectively removed by thermal treatment under H 2 , while heavy coke at the zeolite external surface (external coke) remained intact. This enabled us to analyze the amount, composition, chemical nature, and deactivating effects of internal and external cokes, separately. As the mass transfer of hydrocarbons was retarded with increasing zeolite crystallite size, an aromatic-based catalytic cycle became dominant in MTH compared to an olefin-based cycle. Consequently, methylated benzene intermediates were accumulated within the zeolite micropores. These methylated benzenes could also act as coke precursors and polymerize to form internal coke within the micropores. Aromatic products that diffused out of zeolite micropores could also be condensed at the external surface of the zeolite crystallites. Once the carbon deposits were formed at the external zeolite surface, the external coke continued to grow even non-catalytically by the thermal reaction with the methylated benzenes. Different zeolite catalysts and reaction times affected only the relative amounts of internal and external cokes, but not their respective chemical natures. The internal coke appeared to have the H/C ratio of 1.26 and a density of 1.0 g cm −3 , while the external coke had much lower H/C ratio (0.28) and higher density (1.5 g cm −3 ). We propose that internal coke is likely to have the polymeric structures of the methylated acenes ( i.e ., linearly fused aromatic rings such as benzene, naphthalene, and anthracene) connected via methylene bridges. On the other hand, the external coke is highly polyaromatic with many fused rings. In terms of catalyst deactivation, the internal coke proved to be much more detrimental than the external coke.

Synthesis of clean transportation fuels from syngas (CO + H2) derived from coal, natural gas, and renewable biomass is an efficient method for reducing dependence on oil reservoirs, for which developing effective catalysts is significant. Co-based catalysts supported by carbon materials possess advantages such as longer lifetimes and easy handling of wasted catalysts, but increasing their activity and selectivity remains a challenge. Here we report using Cr as a promoter to enhance the CO hydrogenation process over activated carbon (AC)-supported Co-based catalysts, namely, CoxCr/AC catalysts. An almost twofold increase in activity (from 28.9% to 47.0%), accompanied by decreased CH4, olefin, and alcohol selectivity, was achieved by adding Cr, resulting in a significant increase in the yield of transportation fuel products. The results of chemisorption indicate that Cr facilitates H2 adsorption and suppresses the formation of cobalt carbide (Co2C), forming a relative H-rich and C-lean surface chemical environment, so that the CO hydrogenation process and C–C coupling step are enhanced. Structural characterizations show that Cr exists in the form of Cr2O3 and aggregates on the surfaces of the catalysts in a highly dispersed manner at relative low loadings (

Methylbenzenes entrained within the cavities of silicoaluminophosphate zeotype HSAPO-34 react with methanol in H+-mediated dealkylation to give ethylene and propylene in methanol-to-olefins catalysis. Methylbenzenes dealkylation on solid acids is proposed to occur either via the side-chain mechanism, where an exocyclic C C undergoes successive methylation prior to C C cleavage for olefin elimination, or the paring mechanism, where ring contraction to a bicyclohexenyl cation precedes C C cleavage for olefin elimination. Distinct dealkylation mechanisms prescribe distinct combinations of C atoms—from aromatic methyl, aromatic ring, and methanol/dimethyl ether—to comprise the olefin product. Site-specific isotope tracing that distinguishes between isotope labels in aromatic methyl and aromatic ring positions for each methylbenzene shows that tetramethylbenzene gives ethylene via the side-chain mechanism and penta- and hexamethylbenzene give propylene via the paring mechanism. The ratio of propylene selectivity to ethylene selectivity increases in methanol reactions on HSAPO-34 entrained with a distribution of methylbenzenes deliberately manipulated towards increasing fractions of penta- and hexamethylbenzene, corroborating the conclusion that aromatic precursors and dealkylation mechanisms for ethylene diverge from those for propylene.

The introduction of even low amount of polar functional group is important to expand the range of polyolefin properties. The palladium-catalyzed copolymerization of olefins with polar monomers is a valuable method for the direct synthesis of polar functionalized polyolefins, while low-cost nickel-based catalysts for these copolymerizations still have been limited. Here we report a series of mono- and dinuclear nickel complexes based on structurally simple anilinoanthraquinone ligand for the ethylene copolymerization and norbornene copolymerization with polar monomers. The dinickel catalysts exhibit higher activity and polar monomer incorporation than corresponding mononuclear analogue, owing to the electronic cooperativity effects between the two nickel centers through conjugated ligand.

Co-reaction of methanol and butene was investigated over a high-silica H-ZSM-5 catalyst. It was found that the olefin methylation-cracking and butene dimerization-cracking routes co-occurred, and their contributions depended on the methanol/butene ratio. When more methanol was fed, the olefin methylation-cracking route played a dominant role, producing more propene. An increase in butene amount promoted butene dimerization and the subsequent cracking pathway, improving pentene yield at the expense of ethene, propene, and aromatics. A strong interaction of methanol with butene was observed at a methanol/butene molar ratio of 4:1, resulting in the highest propene selectivity. The spent catalysts were systematically studied by N2 adsorption/desorption, thermogravimetric analysis, Fourier transform infrared spectroscopy, diffuse reflectance UV–vis spectroscopy, Raman spectroscopy and temperature-programmed oxidation techniques. The results reveal that the coke species are mainly formed on the external surface through aromatics methylation and aromatics alkylation with alkene pathways. The increase in the catalytic stability from co-feeding butene is attributed to alleviation of aromatics formation and suppression of the aromatics methylation coking route.

N,O-functionalized and high-temperature-treated carbon nanotubes (N, O, HT-CNTs) were employed to investigate the promotional effects of CNT on Fe catalysts for the Fischer–Tropsch-to-olefins (FTO); particularly, the origin of active sites was explored using multiple in/ex situ techniques. An upward trend in initial activity, olefin selectivity, olefin/paraffin ratio, and chain growth probability is observed in the sequence of O-, N-, and HT-CNT supported catalysts. Unexpectedly, Fe/HT-CNT exhibits superb selectivity of 72.4% to C2–C7 olefins, closing to the Anderson–Schulz–Flory (ASF) limit. The defect-rich electron-withdrawing HT-CNT weakens the reducibility of FeOx and the C3H6 adsorption on Fe, in contrast to O-, N-CNT. The defect-anchored Fe/HT-CNT promotes “Fe-C” formation and phase transformation toward έ-Fe2.2C/e-Fe2C, improving CO adsorption and activation. The above merits boost olefin selectivity on Fe/HT-CNT. However, O-CNT abounded with O groups retards the formation and deep carbonization of the active phase, indicating a gradual increase in the yield.

Isoparaffin-rich gasoline plays an essential role in the global energy consumption. In this regard, there have been extensive studies to prepare catalysts for efficient synthesis of isoparaffin-rich gasoline. In this paper, we report a protocol to incorporate Ni nanoclusters (NiNC) into mesoporous Mes-HZSM-5 zeolite for the synthesis of NiNC@Mes-HZ catalysts. The catalysts are prepared via impregnation of Ni6(PET)12 clusters into Mes-HZSM-5 zeolite, followed by annealing at 550 °C in air. The NiNC@Mes-HZ catalysts are characterized by TEM, XRD, H2-TPR, NH3-TPD, ICP-MS, as well as N2-physical adsorption method. The Ni clusters (average diameter: ca. 1.2–2.7 nm) are found to locate at mesoporous area of the zeolite and interact with Bronsted acid sites of the HZSM-5 zeolite, evidenced by the pyridine adsorption Fourier-transform infrared spectrum analysis. The NiNC@Mes-HZ catalysts (Ni cluster loading = 0.11 wt%) exhibit 100% conversion of dimethyl ether (DME) with 66.4C% selectivity towards C5-11. Results show 53.5C% of C5-11 product contains isoparaffin. This is considerably higher than that for Mes-HZSM-5 zeolite (27.5C% isoparaffin selectivity) and xNiNP@Mes-HZ (73.4% DME conversion) catalysts in the DTG process at 350 °C. The higher selectivity of the 0.11NiNC@Mes-HZ catalysts towards isoparaffin production is deemed to associate with the ease of DTG reaction to take place at the interface of the Ni nanoclusters and acidic sites of the zeolite. Further, it is shown that the nickel nanoclusters largely improve the durability of Mes-HZSM-5 zeolite (over 205 h), which is mainly due to the inhibition of carbon deposition production during the DTG process, evidenced by TPO-MS analysis of the used NiNC@Mes-HZ. The Ni nanoclusters in the zeolite show good hydrogenation capacity and cracking performance, enhancing the olefin methylation pathway on the acidic sites of Mes-HZSM-5 and attenuating the aromatic methylation cycle during the DTG reaction.

Two vanadium complexes bearing amine-bis(phenolate) ligands with the amino side-arm donor, [V{Me2NCH2CH2N(CH2-2-O-3,5-tBu2-C6H2)2}Cl2] (1) and [V{Me2NCH2CH2N(CH2-2-O-3,5-tBu2-C6H2)(CH2-2-O-C6H4)}Cl2] (2), were synthesised and characterized by FTIR and 1H NMR spectroscopy. Upon activation with Al(iBu)3/Ph3CB(C6F5)4, these complexes became active catalysts for 1-octene polymerization giving highly stereoregular polymers (mmmm ∼ 90%) having regioirregularly arranged units. The catalytic activity of the catalysts in ethylene homo- and copolymerization, and their ability to incorporate a comonomer were highly dependent on both the activator type and the complex structure. 1/EtAlCl2 exhibited very high activity (up to 3.3 · 107 g/(molV h)) in ethylene polymerization and produced copolymers with the highest comonomer content (up to 9.1 mol%), moderate molecular weight and narrow chemical composition distribution (CCD). Both vanadium complexes, when combined with trityl borate activator, led to ethylene copolymers with lower 1-octene content and broad CCD. In addition, the copolymers were characterized by very high molecular weight (∼1 · 106 g/mol) and narrow dispersity (Mw/Mn = 1.4–2.0).

Selective synthesis of mixed alcohols from syngas (CO + H2) via Fischer–Tropsch synthesis (FTS) is an alternative one-step one-pot method. Here we report a series of Co-based catalysts supported by activated carbon (AC) and promoted by Mn and La, namely, CoxMnyLa/AC, over which the selectivity to alcohols is usually ∼26.8% and up to 31.7% at elevated reaction pressure, accompanied by a large amount of olefin byproducts (∼30%) that can be further converted to alcohols via a hydroformylation process. Detailed characterizations are performed for the structural properties of catalysts, including physisorption, chemisorption, microscopy, crystal structure, and surface element compositions. The active site of CoxMnyLa/AC catalysts is the highly dispersed metallic Co on the surface of Co2C nanoparticles (Co@Co2C), similar to that of CoxMn/AC catalysts reported previously, while that of CoyLa/AC catalysts is a combination of metallic Co and Co2C phases (Co–Co2C). The result indicates that Mn promoter plays a determinative role in the formation of active sites over CoxMnyLa/AC catalysts. Nevertheless, the La promoter tends to aggregate on the surface of cobalt nanoparticles in the form of La2O3 to promote the CO insertion step and enhance the H2 chemisorption, so that it can both facilitate the formation of alcohols and make the FTS product class shift to light components. The result proves that the structure of active sites can be established by adding a strong promoter such as Mn, and a second promoter, such as La, can be used to tune the FTS reaction toward alcohols by further modifying its surface properties.

Combination of transition metal catalysis with organocatalysis in ways of synergetic catalysis, cooperative catalysis, or/and sequential catalysis has been emerged as a powerful strategy to promote organic transformations that cannot be achieved by each individual independently. Herein, a new protocol for the synthesis of primary amides from olefins, CO and NH3 through one-pot tandem methoxycarbonylation-aminolys was presented over a bi-functional ligand (L1) based rhodium catalyst with functions of co-catalysis. L1 is composed of the phosphino-fragment and the amino-/imino- tautomeric moiety. Then L1-based Rh-catalytic system demonstrated a combination of Rh-P transition metal catalysis and the tautomeric catalysis. In this tandem methoxycarbonylation-aminolysis, NH3 also served as a ligand to work together with the phosphino-fragment to synergetically modify the performance of Rh-catalyst responsible for the first-step methoxycarbonylation of olefin to generate the esters, and the Rh-tailed tautomeric catalyst was in charge of the subsequent aminolysis to generate the targeted primary amides.

Immobilized catalysts were prepared by mixing the ligand Cp′, [C5Me4(n-propyl-Si(OEt)3)], with RhCl3·xH2 O for subsequent reaction with silica Aerosil 200 (system A) or by copolymerization with TEOS (system B). Both systems were applied on olefin hydrogenation, showing high activity and robustness, allowing for many recycles (TON = 1.0 × 10 5 for system A and 2.0 × 104 for system B). The characterization techniques (IR-DRIFTS, 13C-CPMAS, and TEM) suggest a molecular nature for catalytic species. According to the deuteration experiment, a tetra-hapto-Cp′-Rh would be formed on the surface during the catalytic runs.

We report a facile hydrothermal synthesis of nanorod-structured molybdenum-tungsten oxides as an efficient catalyst for olefin hydrogenation. The catalytic activity was demonstrated through hydrogenation of cyclohexene used as a model system. The as-prepared material was confirmed as a new phase (Mo0.6W0.4O3) via a series of characterizations, instead of a simple mixture of MoO3 and WO3. The Mo0.6W0.4O3 catalyst displays excellent catalytic activity with 100% conversion of cyclohexene in 3 h, which is much higher than that of pure MoO3 and pure WO3 synthesized with the same method. It was found that hydrogen bronze (HxMo0.6W0.4O3) was formed during the hydrogenation process, and the catalytic performance was positively correlated with the hydrogen content. The obtained nanorod-structured Mo0.6W0.4O3 without loading any noble metal exhibits much higher catalytic activity than a Pd/MoO3 catalyst. The results demonstrate that the nanorod-structured molybdenum-tungsten oxide may be a strong contender for serving as an efficient hydrogenation catalyst alternative to precious metals.

Au nanoparticles (AuNPs) were immobilized on S-containing amino acids (cysteine and methionine) Mg/Al hydrotalcite clay in both bulk and exfoliated (colloidal) forms. The Au nanoparticles were prepared by a biomimetic method using an anti-oxidant tea extract to reduce the Au salt solution. The performance of bulk and exfoliated clays with Au nanoparticles in aerobic olefin epoxidation was assessed with very interesting results. Both catalysts were very active towards the epoxide products; selectivity was found to be dependent on the catalyst form. The exfoliated catalysts yielded higher product stereoselectivity in the case of limonene epoxidation. These results can be explained by the existence of a confined environment around the AuNPs structures provided by the clay nanosheets wrapping the nanoparticles, modulating how substrates interact with the catalytic active centres. Based on experimental data mechanistic proposals were also rationalized for these catalysts showing how they assist the catalytic process.

A monotonic increase (2–18) in the effluent propylene-to-ethylene molar ratio as inlet methanol pressure is varied from 52.5 to 0.6 kPa during methanol-to-hydrocarbons catalysis (∼30%C conversion) on H-ZSM-5 at 673 K reveals methanol pressure as the salient process parameter that allows control over the relative rates of propagation of the olefins- and aromatics-based methylation/cracking events. The enhanced propagation of the olefins-based cycle over its aromatics-based counterpart and consequently, decoupling of the two catalytic cycles at low influent methanol pressures is observed to persist irrespective of the reaction temperature (623–773 K). Reactions involving formaldehyde co-feeds (3–20 Pa or 0.5–5%C) with low-pressure (0.6 kPa) methanol at 623 K result in a monotonically decreasing trend in propylene-to-ethylene molar ratio from 24.7 in the absence of formaldehyde to 0.8 in the presence of 20 Pa formaldehyde implicating suppressed formaldehyde production from methanol transfer dehydrogenation events at low methanol pressures as the mechanistic basis for the observed effect of enhanced olefin cycle propagation. Co-reacting formaldehyde (11 Pa or 3%C) with propylene (0.1 kPa) on H-ZSM-5 at 623 K results in a 5.5-fold increase in aromatics selectivity suggesting Prins condensation reactions between formaldehyde and olefins are likely involved in aromatics production during methanol-to-hydrocarbons catalysis over H-ZSM-5.

A nitrogen-doped carbon-supported cobalt oxide catalyst is able to oligomerize ethylene, propylene, 1-butene and 1-hexene into mixtures of oligomers with above 94.1% dimers. Higher than 72.5% of the dimers produced from 1-butene and 1-hexene are internal linear olefins, while the dimer products from propylene oligomerization are 47.0% linear including 5.9% 1-hexene. Ethylene had the highest oligomerization activity with 56.1–87.0% 1-butene selectivity. The selectivity to linear alpha olefins decreases with an increasing oligomer chain length during ethylene oligomerization. The oligomers formed from ethylene conversion follow a Schulz-Flory distribution. Cossee type mechanism rationalizes the product selectivity from the four olefin feeds, suggesting that a 1,2-2,1 insertion sequence is critical to obtaining linear olefin products. The catalyst was inactive in oligomerizing internal olefins.

Silica-supported well-defined Cr(III) sites, which polymerize ethene, are barely reactive towards propene while they copolymerize propene and ethene, a reactivity pattern similar to what is observed for the Phillips catalyst. In contrast to ethene, propene is only polymerized in low amounts and by a small fraction of sites, while during propene/ethene copolymerization small amounts of olefinic oligomers are formed. This difference of reactivity pattern among various olefins is further examined by DFT calculations using periodic amorphous models, focusing on the initiation of polymerization by olefin insertion into the Cr O bond vs. the heterolytic C H activation of the alkene. For both mechanisms, we found that the initial activation displays similar energetics for propene and ethene, while the subsequent propene insertion associated with chain growth becomes rather demanding, which rationalizes the observed difference of reactivity between ethene and propene.

A chiral MnIII-porphyrin complex covalently bonded with mesoporous SBA-15 (SBA15-[Mn(TCPP-R∗)Cl]) was synthesized and fully characterized. The heterogeneous SBA15-[Mn(TCPP-R∗)Cl] exhibited remarkable catalytic activity toward enantioselective olefin epoxidation using O2 as terminal oxidant in the presence of isobutyraldehyde. The catalyst showed higher enantioselectivity than its homogeneous counterpart in the oxidation of α-methylstyrene. SBA15-[Mn(TCPP-R∗)Cl] catalyzed epoxidation of styrene was achieved within 8 h and optically active styrene oxide was obtained in 89% ee and 90% yield. Likewise, styrene derivatives (trans-β-methylstyrene, indene), conjugated cis- and trans-disubstituted olefins (e.g. cis- and tans-stilbene) and terminal olefins were converted effectively to their corresponding epoxides in 63–99% ee under the Mn(III)-catalyzed conditions. The catalyst could be recycled five times without any significant loss in activity.

Fischer–Tropsch synthesis (FTS) is a key technology for the production of liquid fuels from syngas. Enhanced liquid fuel production and catalytic stability can be achieved by rational design of catalysts Due to the metal–promoter interaction, conventional Mn-modified ion-based catalysts showed high C2 through C4 olefin selectivity and low activity. In this paper, Mn-containing SiO2-encapsulated ion-based double-shell spindles were fabricated and employed as a FTS catalyst. For the proposed design, the SiO2 shell not only is employed as an interlayer to weaken the contact between Fe and the Mn promoter, but also acted as the anchoring site for Mn nanoparticles. The results showed that the Mn-modified FeSiMn catalyst presents higher catalytic activity (3.41 × 10−5 molCO gFe−1 s−1) and superior C5+ production (20.8 × 10−4 gHC gFe−1 s−1) compared to the unmodified FeSi catalyst. This can be ascribed to the Mn-improved spillover effect. Thus, design of double-shell catalysts provides important clues for understanding the sole effect of the promoter on catalytic performance and for improving the production of liquid fuels.

The factor dominating olefin to paraffin ratio in cobalt-catalyzed Fischer-Tropsch synthesis has been identified via experimental kinetic studies and theoretical calculations including the van der Waals interaction between the adsorbates and Co surfaces. The olefin to paraffin ratio for each carbon number is expressed as a function of adsorption energies of olefin and activation energies of hydrogenation steps. Density functional theory calculations on Co (0 0 0 1) surface were performed to provide a comprehensive fundamental insight for the chemistry governing the olefin to paraffin ratio. The calculated olefin to paraffin ratio decreases with chain length except for ethylene, which agrees well with the experimental results. The differences introduced to the adsorption energies of olefin by van der Waals functional are correlated with d-band center changes of the Co surface. The carbon number dependent adsorption energies of olefin, rather than the activation energies of their hydrogenation reactions, are the driven force for the carbon number dependent olefin to paraffin ratio. The insights may delineate a new blueprint for the rational design of catalysts with enhanced olefin to paraffin ratio.

The selective epoxidation of olefins with hydrogen peroxide (H2O2) over transition metal substituted zeolites is less environmentally impactful than epoxidation schemes that use chlorinated or organic oxidants. The structure and reactivity of reactive intermediates derived from H2O2 and the mechanism for olefin epoxidation on such materials are debated. Here, cyclohexene oxide formation and H2O2 decomposition rates (measured as functions of reactant and product concentrations) and in situ infrared (IR) and UV-vis spectroscopy are used to probe the intervening elementary steps for cyclohexene (C6H10) epoxidation and the identity of the reactive intermediates on a Nb-β catalyst. IR and UV-vis spectra acquired in situ show that the reactive intermediates are predominantly superoxide species (NbIV-(O2)−, observed also by X-ray photoelectron spectroscopy), which form by the irreversible activation of H2O2 over Nb centers. Similar M-(O2)∗ (M = Ti or Ta) intermediates were previously assumed to form via reversible processes; however, in situ IR and UV-vis measurements directly show that NbIV-(O2)− forms irreversibly in both H2O and acetonitrile. Activation enthalpies (ΔH‡) for C6H10 epoxidation are 27 kJ mol−1 higher than for H2O2 decomposition, while activation entropies (ΔS‡) for epoxidation are 56 J mol−1 K−1 lower than for H2O2. These comparisons show that the selectivities for epoxidation, via primary reaction pathways, increase with increasing reaction temperatures. Collectively, these results provide a self-consistent mechanism for C6H10 epoxidation that is also in agreement with previously published data. These findings will aid the rational design and study of alternative metal oxide catalysts for olefin oxidation reactions.

The efforts to obtain superior active and long-lived practical zeolite catalysts must be based on shaped forms rather than only powder, if considering necessary mechanical strength requirement in industrial application. The binders, incorporated as indispensable additives to keep intact of macroscopical body, are catalytically inert and their negative impacts in mass transfer are widely neglected. Here, we firstly revealed the remarkable mass transfer depression by incorporating silica sol as binders in shaped zeolitic catalyst. Then, by re-crystallizing the shaped binder/zeolite body with assistance of controlled organic template steam, the binders were converted into zeolitic phase, forming full-zeolitic monoliths. In re-crystallization, it was found obvious intra-crystalline mesopores were in situ created while maintaining high mechanical strength. A remarkable mass transfer advantage was revealed in such hierarchical monolith, which means more acid sites will be accessible after re-crystallization. Therefore, in performance evaluation, hierarchical full-zeolitic monolith demonstrated higher propylene yield and slower deactivation rate in C4 olefin cracking reaction. Moreover, highly prolonged cycle time, which was more than 2000 h and three times as long as that of commercial catalyst, was realized in catalyzing methanol-to-hydrocarbons (MTH) under industrial condition. That is the first report on so long-lived zeolite catalyst without regeneration in methanol conversion reaction. Fundamental understanding in re-crystallization of monolithic material will contribute significantly to technical progress in developing more high-valued applicable catalysts and optimizing existing zeolite catalyst.

The formation and reactivity of a methylbenzenes (MBs) hydrocarbon pool in the induction period of the methanol-to-olefins (MTO) reaction over zeolite H-ZSM-5 was investigated and the mechanistic link of MBs to ethene and propene was revealed. Time evolution analysis of the formed MBs and C-12/C-13 methanol-switching experiments indicate that in the induction period bulkier compounds such as tetraMB and pentaMB have higher reactivity than their lighter counterparts such as p/m-diMB and triMB. By correlating the distribution of MBs trapped on H-ZSM-5 with ethene and propene, we found that tetraMB and pentaMB favor the formation of propene, while p/m-diMB and triMB mainly contribute to the formation of ethene. On the basis of this relationship, the olefin (ethene and propene) selectivity can be controlled by regulating the distribution of trapped MBs by varying the silicon-to-aluminum ratio of ZSM-5, reaction temperature, and space velocity. The reactivity of MBs and the correlation of MBs with olefins were also verified under steady-state conditions. By observation of key cyclopentenyl and pentamethylbenzenium cation intermediates using in situ solid-state NMR spectroscopy, a paring mechanism was proposed to link MBs with ethene and propene. P/M-diMB and triMB produce ethylcyclopentenyl cations followed by splitting off of ethene, while tetraMB and pentaMB generate propyl-attached intermediates, which eventually produce propene. This work provides new insight into the MBs hydrocarbon pool in MTO chemistry. (C) 2015 Elsevier Inc. All rights reserved.

NMR study of the oxidation of several Mo(II) precatalysts [CpMo(CO) 3 R] (R = CH 2 COOC 2 H 5 1 , CH 2 COOBornyl 5 , CH 3 6 , CH 2 C 6 H 5 7 , CH 2 C 6 F 5 8 ) with tert -butylhydroperoxide (TBHP) in CDCl 3 at 22 °C shows the formation of complexes [CpMoO 2 R] ( I ), [CpMo(O)(η 2 -O 2 )R] ( II ) and transient species assigned as A and B . ν(Mo O Mo) at 678 and 655 cm −1 are identified during oxidation of 5 monitored by in situ IR. DFT calculations for R = CH 2 COOCH 3 indicate that the involvement of [CpMo IV (O)R], I 0 and [(CpMo V (O)R) 2 (μ-O) 1,2 ], ( M ox1,2 ) species in various oxidative transformations is energetically feasible. Oxidative decarbonylation of 5 at different reaction temperatures and oxidant and precatalyst concentrations has also been studied. IR and mass spectroscopic analysis of the precipitate obtained from oxidation of 5 suggests that it is an oxomolybdenum species without ligand R. NMR study of catalytic epoxidation of cis -cyclooctene using 1 illustrates the inhibitory effect of the substrate on oxidative transformations of the precatalyst.

The effect of temperature, pressure, and solvent on 1-butene oligomerization was studied over H-ferrierite. Two-dimensional GC (GC×GC–MS) was used to analyze the olefin, paraffin, aromatic, and cycloalkane products of the C4 olefin conversion. The reaction product mixture revealed H-ferrierite promoted double bond isomerization, skeletal isomerization, oligomerization, hydrogen transfer, cyclization and cracking reactions. The double bond isomerization reaction reached equilibrium for both C4 and C8 olefins. Primary products from C4 olefin dimerization were 3,4-dimethyl-2-hexene and 3-methyl-2-heptene. The oligomerization products followed the Schulz–Flory chain growth distribution. The chain growth distribution is a function of the C4 olefin conversion. Most of the heavier olefins (>C12) were highly branched (>trimethyl- and methyl-ethyl-species). The selectivity towards oligomerization products was maximized at low temperatures (below 473 K). At temperatures above 473 K olefins underwent cracking and hydride transfer reactions to produce olefins, paraffins, and aromatics. Co-feeding hexane solvent increased C4 olefin conversion and led to a shift of product distribution from heavier to lighter species. The medium pores were relatively stable for production of longer chain olefins (C6–C20) from C4 olefins near supercritical conditions. The reaction rate was second order in the near-critical region. The deactivation rate decreased with increasing 1-butene partial pressure.

Two novel cyclopentadienyl molybdenum complexes [CpMo(CO) 2(ImPyMes)Cl] (1) (ImPyMes = 2-mesitylimidazo[1,5-a]pyridine-3-ylidene) and [CpMo(CO)2(ImPyMes)(NCCH3)]BF4 (2 ) were employed as pre-catalysts in olefin epoxidation catalysis using tert-butylhydroperoxide (TBHP) as oxidant. Turnover frequencies (TOFs) of 40,900 h−1 (0.005 mol% 1) and 53,100 h−1 (0.01 mol% 2) were achieved in cis-cyclooctene epoxidation in CHCl3 at 55 °C, outperforming most previously reported Mo epoxidation catalysts. The synthesis of 1 proceeds via the silver carbene transmetallation route in 90% yield, and further treatment of 1 with AgBF4 in CH3CN leads to the ionic complex 2 in 87% yield. Even at very low pre-catalyst concentrations, quantitative cis-cyclooctene conversion with high selectivity is achieved. Furthermore, epoxidation of more challenging substrates results in good conversions and recycling experiments in room temperature ionic liquid (RTIL) [C8mim]NTf2 (C8mim = 1-methyl-3-octylimidazolium, NTf2 = bis(trifluoromethanesulfonyl)imide) shows reusability of 1 in catalytic epoxidation for several runs without loss of activity.

The underlying mechanisms of the two distinct catalytic cycles operating during conversion of methanol to olefins (MTO) on HZSM-5 have been elucidated under industrially relevant conditions. The co-existence of olefins and aromatic molecules in the zeolite pores leads to competition between the two cycles. Therefore, their importance depends on the local chemical potential of specific carbon species and the methanol conversion. Due to a faster, “autocatalytic” reaction pathway in the olefin based cycle, olefin homologation/cracking is dominant under MTO conditions, irrespective of whether aromatic molecules or olefins are co-fed with methanol. Another hydrogen transfer pathway, faster than the usual route, has been identified, which is directly linked to methanol. In agreement with that, the co-feeding of olefins resulted in a remarkable longer lifetime of the catalyst under MTO conditions, because the high rate methylation competes with the formation of more deactivating coke – presumably oxygenates- through methanol derivatives.

Our mechanism for the methanation reaction pathway (Govender et al., 2008) during the Fischer–Tropsch synthesis at high-temperature reaction conditions (330 °C, H 2 /CO = 15 and 1.2 bar) is extended here to account for the formation of C 2+ hydrocarbons. The C 2 and C 3 hydrocarbon transients derived from 13 CO SSITKA experiments were used to discriminate between three mechanistic models. It is shown that a mechanism with two surface intermediates for the C 2+ hydrocarbons and with olefin readsorption directly to the corresponding paraffin surface intermediate describes the data the best. Parameter estimates for the rate constants describing the formation of the C 2 are reported. The optimal model is also shown to fit the C 3 hydrocarbons. The SSITKA measurements were also used to determine surface coverages and the turnover frequency. We propose C s and C s H as the active C 1 species with both participating in chain initiation to form reactive C 2 species such as C s C s H.

Silver is credited with being a unique catalyst for direct epoxidation of ethene. Copper(II) oxide is known for its combustion catalytic properties in such reactions. In this paper it is reported for the first time that copper oxides under certain conditions can catalyze direct epoxidation of ethene. Reduced copper oxide, ethene, and molecular oxygen are the minimum necessary and sufficient conditions for olefin epoxidation. There is an induction period for the onset of epoxidation. On continual use of this mixed oxide, the selectivity diminishes progressively to about 1%. Reduction of the used mixed oxide restores selectivity, at least in part. A two-stage pulsed reaction (alternating pulses of hydrogen and oxygen in flowing ethene) maintains the selectivity, suggesting that the active species in epoxidation reaction is close to the Cu(I) state. It is also possible to maintain this active species for the sustained reaction by adjusting the oxygen partial pressure to be close to 0.07.

Helical mesoporous materials of the MCM-41 type are important materials that can be prepared by onepot synthesis procedures with a co-surfactant. A control of the characteristics at a local level is of the most important in the view of the applications of such materials. However, there are not many studies relating such features with synthetic approaches. In this work, we prepared both helical and regular channel materials from Si-based MCM-41 type. Afterward, a bpy derivative was used as ligand to coordinate MoII/VI. The complexes and the new materials were tested as the catalytic precursors in the epoxidation of cis-cyclooctene, styrene, 1-octene, R-(+)-limonene and trans-hex-2-en-1-ol, using tert-butylhydroperoxide (TBHP) as oxidant. Although almost all the catalysts were 100% selective toward the epoxide, the conversions were in general good. The major achievement of these catalysts is an outstanding stereocontrol of the reaction products. In addition, these catalysts were found to be very effective under several circumstances. This is certainly an important contribution for such concept and may render such materials further applications where chiral recognition is important.

The methanol to olefins process is an alternative for oil-based production of ethene and propene. However, detailed information on the reaction mechanisms of olefin formation in different zeolite is lacking. Herein, a first-principle kinetic study allows elucidating the importance of a side-chain mechanism during methanol conversion in H-SAPO-34. Starting from the experimentally observed hexamethylbenzene, a full low-barrier catalytic cycle for ethene and propene formation is found. The olefin elimination steps exhibit low free energy barriers due to a subtle interplay between a sp3 carbon center of the organic intermediate, stabilizing non-bonding interactions and assisting water molecules in the zeolite material.

We investigated acid-catalyzed dimerization for C8 to C24 linear olefins on Amberlyst® 15 at 90 °C. Double bond position and monomer chain length had no effect on dimerization rate of linear monomers. Dimerization was first order in both monomer and catalyst and occurred via an Eley–Rideal mechanism, in which adsorbed monomer reacted with olefin in the bulk phase. Relative dimerization rates between competing monomers of different chain lengths depended solely upon relative adsorptions of the competing monomers, as all linear olefins reacted equally well with any adsorbed monomer. Relative adsorption onto dimerization sites decreased markedly as chain length increased from C8 to C14, but there was no observed change in adsorption coefficients as chain length increased from C14 to C24. Trimerization occurred when bulk dimer reacted with adsorbed monomer. Dimer molecules competed well for dimerization sites and inhibited the rate of monomer dimerization. The rate-limiting step in dimer formation was the reaction of bulk olefin with adsorbed monomer.

The observed product distribution in methanol-to-hydrocarbons (MTH) catalysis can be rationalized based on the relative rates of propagation of the aromatic- and olefin-based cycles that operate on the zeolite catalyst. We report that the ratio of ethene to 2-methylbutane + 2-methyl-2-butene (ethene/2MB) yield can be used to describe the propagation of aromatic and olefin methylation/cracking cycles. The co-reaction of 12C-ethene with 13C-dimethyl ether (DME) shows that the rate of DME conversion (1.62 mol C (mol Al s)−1) is ∼20 times faster than ethene conversion (0.08 mol C (mol Al s)−1), suggesting that ethene can be considered as terminal product for MTH at 623 K. At iso-conversion conditions at 548 K, propene is co-fed with DME to increase propagation of the olefin-based cycle and correspondingly a 1.7-fold decrease in the ethene/2MB yield is observed. Similarly, the co-reaction of toluene with DME increases propagation of the aromatic-based cycle and a 2.1-fold increase in the ethene/2MB yield is observed. The ethene/2MB yield also increased by a factor of 2 as DME conversion increased from 5% to 62%, which is consistent with the observed concurrent increase in selectivity to ethene and methylbenzenes. For the reaction of DME alone, increasing the temperature from 548 K to 723 K increases the propagation of the olefin-based cycle and a corresponding decrease in the ethene/2MB yield from 4.7 to 1.3 is also observed. The ethene/2MB yield varies systematically with feed composition, conversion, and temperature, showing that this ratio describes the relative propagation of the aromatic to olefin methylation/cracking cycles in MTH conversion on H-ZSM-5.

Light olefin oligomerization is an important alternative for the production of clean liquid automotive fuels and can be performed in the presence of solid acid catalysts. Among these, medium-pore zeolites, and especially ZSM-5, have been widely described in the open literature. In this work, the relative importance of intracrystalline diffusion path lengths for the product molecules (depending on the zeolite crystal size and the presence of mesopores in the crystallites) and Bronsted acid site density are discussed for two different olefins, propene and 1-pentene. Thus, ZSM-5 samples with (a) the same crystallite size and different acid site density, (b) the same density of acid sites and different crystallite size, (c) postsynthesis generation of mesopores by different desilication severities, and (d) samples with similar crystal size, mesoporosity, and acid site density, but with a different ratio of external to internal acid sites have been prepared and studied for oligomerization of propene and 1-pentene. The results obtained suggest that the properties required for a best-performing catalyst (maximum conversion and lowest deactivation rate) are different for these two alkenes. Whereas Bronsted acid site density is determinant for propene oligomerization when intracrystalline diffusion path lengths are below a certain critical value, the presence of a large number of Bronsted acid sites is not sufficient in the case of 1-pentene, and additional mesoporosity becomes crucial. Thus, mesoporous ZSM-5 samples prepared by postsynthesis desilication treatments present a greater improvement in initial conversion and catalyst life for 1-pentene oligomerization than for conversion of propene.

Identifying the active site on the surface of a heterogeneous catalyst is one of the biggest challenges in the field of catalysis research. Especially, in the case of structure sensitive and heterogeneously catalyzed reactions, the knowledge of the active site/ensemble would result in a great advantage in the quest to design tailored catalyst displaying the desired activity and selectivity. In the Fischer–Tropsch synthesis, the multitude of reaction products as well as the large number different reaction pathways does result in additional difficulties in the search for the active site/ensemble. In the here presented work, we were able to conduct a thorough study of the CO hydrogenation reactions on nano-sized alumina supported cobalt crystallite model catalysts. By evaluating the full product spectrum, it was possible to deconvolute the structure sensitivity of the various reactions and to gain further insight into the nature of the present reaction mechanisms. It was therefore possible to measure decreasing carbon monoxide turn over frequency with decreasing cobalt crystallite site, paralleled with an increased selectivity toward methane and branched hydrocarbons at a constant olefin selectivity. Although these trends were observed to be independent of time on stream, the activity did change drastically upon the initial exposure to reaction conditions. CO-TPD studies provided direct evidence for the observed size dependencies.

The reaction intermediates of methanol-to-olefin (MTO) conversion over phosphorous-modified HZSM-5 (P-MFI) catalysts were investigated by electron spin resonance (ESR) and gas chromatography–mass spectroscopy (GC–MS). Phosphorous modification partially neutralized the strong acid sites in HZSM-5. The phosphorous compounds suppress the migration of polymethylbenzenium radical cations, lowering spin–spin interactions and thus preserved their hyperfine splitting. The ESR spectra of the organic species formed in P-MFI zeolites during MTO conversion were similar to those of the cation species generated from 1,2,4,5-tetramethylbenzene in mordenite. GC–MS of organic extracts revealed the predominant formation of polymethylbenzenes with 4–6 methyl groups. The correlation between conversion and the number of spins of tetramethylbenzenium radical cations exhibited that these radical cations might be major active intermediates of MTO conversion over P-MFI catalysts.

Methyl isobutyl ketone (MIBK) can be viewed as a key intermediate for the conversion of biomass-derived acetone – the by-product of biobutanol production – to transportation fuel. Zeolite H-ZSM-5 doped with Pt nanoparticles was found to be a highly efficient catalyst for gas-phase hydrogenation of MIBK to methylpentanes with >99% yield at 200 °C. The reaction proceeds via bifunctional metal-acid catalysed pathway involving MIBK hydrogenation to 4-methyl-2-pentanol (MP-ol) on metal sites followed by MP-ol dehydration on acid sites to form olefin and finally olefin hydrogenation to 2-methylpentane (2MP) on metal sites, with all three steps occurring on a single catalyst bed. 2MP thus obtained underwent isomerisation over bifunctional Pt/H-ZSM-5 catalyst to give a mixture of 2- and 3-methylpentanes in a ratio of 83:17. The catalyst did not show any deactivation for at least 16 h on stream.

The product selectivity of dimethyl ether (DME) conversion to hydrocarbons on H-ZSM-5 was systematically tuned by co-feeding small amounts of 13 C-propene and 13 C-toluene (4 kPa) with 12 C-DME (70 kPa) under isoconversion conditions (20.8–22.7 C%) at 548 K. The selectivity to ethene (14.5–18 C%) and aromatics (7.1–33.7 C%) increased while selectivity to C 4 –C 7 aliphatics (42.8–16.9 C%) decreased with increasing amounts of toluene (0–4 kPa) in the co-feed. Similar trends were also observed at lower conversions (4.6–5.1 C%) at 548 K and at higher temperatures (623 K), showing that the olefin-to-aromatic ratio can be used as a parameter to propagate the olefin- and aromatic-based carbon pools to varying extents within the range of conditions studied in this work. The co-reaction of 13 C-propene with 12 C-DME showed that C 5 –C 7 olefins are formed almost exclusively from methylation reactions while butenes are formed from both olefin cracking and methylation reactions. The high fraction of propene (55.1%) with at least one 12 C indicated that a large fraction of propene is a product of olefin cracking reactions. Under conditions in which the aromatic-based cycle is dominant (increasing amounts of toluene in the co-feed), both ethene and propene contained approximately 10% 13 C atoms, showing that when the olefin-based cycle is suppressed, these light olefins primarily originate from the aromatic-based cycle. The 13 C content of toluene in the effluent was unchanged compared to that in the 13 C-toluene feed, implying that toluene is not formed as a significant product. Additionally, at least 9.8% of p -xylene, 1,2,4-trimethylbenzene, and 1,2,4,5-tetramethylbenzene isotopomers were entirely 12 C-labeled, while less than 2% of toluene and o -xylene isotopomers were entirely 12 C-labeled, showing that under the conditions studied in this work, cyclization reactions occur predominantly for C 8+ aliphatics to form p -xylene and larger aromatics. Because the olefin- and aromatic-based cycles are not isolated from one another, understanding communication between the two cycles is an important step in controlling selectivity of MTH on H-ZSM-5.