Catalysts For Ammoxidation Research Articles

Manganese Carbodiimide (MnNCN): A New Heterogeneous Mn Catalyst for the Selective Synthesis of Nitriles from Alcohols

Earth‐abundant manganese oxides (MnOx) were competitive candidates when screening catalysts for ammoxidation of alcohols into nitriles due to their redox property. However, over‐oxidation and possible acid‐catalyzed hydrolysis of nitriles into amides still limited the application of MnOx in nitrile synthesis. In this work, manganese carbodiimide (MnNCN) was first reported to be robust for the ammoxidation of alcohols into nitriles, avoiding over‐oxidation and the hydrolysis. Besides the high activity and selectivity, MnNCN demonstrated wide substrate scope including the ammoxidation of primary alcohols into nitriles, the oxidative C‐C bonds cleavage and ammoxidation of secondary alcohols, phenyl substituted aliphatic alcohols, and diols into nitriles. Controlled experiments and DFT calculation results revealed that the excellent catalytic performance of MnNCN originated from its high ability in the activation of O2 molecules, and favorable oxidative dehydrogenation of C=N bonds in the aldimine intermediates (RCH=NH) into nitriles, inhibiting the competitive side reaction of the oxidation of aldehydes into carboxylic acids, followed to amide byproducts. Moreover, the hydrolysis of nitriles was also inhibited over MnNCN for its weak acidity as compared with MnOx. This study provided new insights into Mn‐catalyzed aerobic oxidations as a highly important complement to manganese oxides.

Manganese Carbodiimide (MnNCN): A New Heterogeneous Mn Catalyst for the Selective Synthesis of Nitriles from Alcohols.

Earth-abundant manganese oxides (MnOx) were competitive candidates when screening catalysts for ammoxidation of alcohols into nitriles due to their redox property. However, over-oxidation and possible acid-catalyzed hydrolysis of nitriles into amides still limited the application of MnOx in nitrile synthesis. In this work, manganese carbodiimide (MnNCN) was first reported to be robust for the ammoxidation of alcohols into nitriles, avoiding over-oxidation and the hydrolysis. Besides the high activity and selectivity, MnNCN demonstrated wide substrate scope including the ammoxidation of primary alcohols into nitriles, the oxidative C-C bonds cleavage and ammoxidation of secondary alcohols, phenyl substituted aliphatic alcohols, and diols into nitriles. Controlled experiments and DFT calculation results revealed that the excellent catalytic performance of MnNCN originated from its high ability in the activation of O2 molecules, and favorable oxidative dehydrogenation of C=N bonds in the aldimine intermediates (RCH=NH) into nitriles, inhibiting the competitive side reaction of the oxidation of aldehydes into carboxylic acids, followed to amide byproducts. Moreover, the hydrolysis of nitriles was also inhibited over MnNCN for its weak acidity as compared with MnOx. This study provided new insights into Mn-catalyzed aerobic oxidations as a highly important complement to manganese oxides.

Optimizing Selectivity in VOx/TiO2 Catalysts for Ammoxidation: Insights from Structure–Performance Relationships

Optimizing Selectivity in VO_<i>x</i>/TiO₂ Catalysts for Ammoxidation: Insights from Structure–Performance Relationships

Catalytic performances of VPO/SBA-15 catalysts for ammoxidation of dichlorotoluenes

Catalytic performances of VPO/SBA-15 catalysts for ammoxidation of dichlorotoluenes

Tridoped Mesoporous Carbon as a Metal-Free Catalyst for Ammoxidation of (Hetero)Aromatic Alcohols to Nitriles

Tridoped Mesoporous Carbon as a Metal-Free Catalyst for Ammoxidation of (Hetero)Aromatic Alcohols to Nitriles

Vanadium–phosphorous oxide supported on mesoporous SBA-15 catalysts for ammoxidation of toluene to benzonitrile

Reaction scheme of ammoxidation of toluene over VPO/SBA-15.

Efficient iron single-atom catalysts for selective ammoxidation of alcohols to nitriles

Zeolitic imidazolate frameworks derived Fe1-N-C catalysts with isolated single iron atoms have been synthesized and applied for selective ammoxidation reactions. For the preparation of the different Fe-based materials, benzylamine as an additive proved to be essential to tune the morphology and size of ZIFs resulting in uniform and smaller particles, which allow stable atomically dispersed Fe–N4 active sites. The optimal catalyst Fe1-N-C achieves an efficient synthesis of various aryl, heterocyclic, allylic, and aliphatic nitriles from alcohols in water under very mild conditions. With its chemoselectivity, recyclability, high efficiency under mild conditions this new system complements the toolbox of catalysts for nitrile synthesis, which are important intermediates with many applications in life sciences and industry.

Understanding the role of Al2O3-ZrO2 mixed oxides as support for vanadium catalysts for the selective ammoxidation of o-chlorotoluene to o-chlorobenzonitrile

o-Chlorotoluene (o-CT) ammoxidation to prepare o-chlorobenzonitrile (o-CBN) was investigated on Al2O3-ZrO2 supported V2O5 catalysts in the temperature range of 360 to 420 °C. A set of vanadium oxide supported on mixed oxides with varying its loadings were prepared by wet impregnation method. The catalysts surface and structural characteristics were derived from BET-surface area, X-ray diffraction, FT-infrared, temperature programmed reduction, temperature programmed desorption of ammonia and UV–Vis diffuse reflectance spectroscopy. The characterization results revealed that vanadium species were well dispersed and strongly interacted with mixed oxide support. The ammoxidation activity was depended on V2O5 content and its nature of surface species existing in the catalyst. The catalyst with 10 wt% of V2O5 on Al2O3-ZrO2 showed high ammoxidation activity with 100% selectivity to o-CBN. Moreover, the catalyst showed consistent activity during time on stream study.

Thermally stable imidazole/heteropoly acid composite as a heterogeneous catalyst for m-xylene ammoxidation

Ammoxidation of m-xylene is evaluated in the presence of a customized heteropoly acid catalyst as an imidazole/molybdovanadophosphoric acid (imidazole/PMoV). Imidazole is employed to maintain its heterogeneous phase during the ammoxidation reaction and to provide the thermal stability of PMoV with the expectation that imidazole can generate strong electronic interactions with terminal molybdenum-oxygen on PMoV. The characterizations of the prepared catalysts are performed using SEM–EDX, XRD, FT-IR, Raman, XPS, and TGA to prove the physical and chemical changes by incorporating imidazole to PMoV, respectively. Also, the thermal stability of the developed catalyst is confirmed by the means of heat treatment test at relatively high temperature. The composite catalyst, imidazole/PMoV, shows an excellent conversion rate of over 98% with high selectivity of isophthalonitrile in m-xylene ammoxidation. Moreover, while the imidazole-free PMoV catalyst is deactivated and washed out during the reaction, the catalyst durability of the imidazole/PMoV is preserved without significant activity loss after 5 reaction cycles at 380 °C.

Highly selective Sn/HZSM-5 catalyst for ethane ammoxidation to acetonitrile and ethylene

The ammoxidation of ethane over the conventional metal oxide and Co/zeolite catalysts faces the challenge of inadequate selectivity owing to the formation of CO2, N2, and NOx. Here we report that Sn modified ZSM-5 catalyst is highly selective for ethane ammoxidation. The C- and N-based acetonitrile selectivities are up to 80 % and 70 % over the Sn/HZSM-5, but they are below 60 % and 20 %, over the Co/HZSM-5. We suggested that the Sn (IV) cations are the critical active sites for acetonitrile formation, and the presence of nanosized SnOx particles favors CO2 formation. Transient kinetics analysis suggested that ethane ammoxidation over the Sn/HZSM-5 follows the same reaction pathways as that over the Co/HZSM-5. However, the surface abundancy of the reaction intermediates over these two catalysts is different, which could be the reason for the enhanced selectivity over the Sn (IV) cations in contrast to the Co (II) cations in the ZSM-5 zeolite.

Clariant, TechnipFMC test acrylo catalysts

Clariant and the engineering firm TechnipFMC will work together to commercialize Clariant’s AcryloMax propylene ammoxidation catalysts, which are used for making acrylonitrile. Clariant says its ne...

Earth-Abundant Bimetallic Nanoparticle Catalysts for Aerobic Ammoxidation of Alcohols to Nitriles.

Heterogeneous nitrogen-doped carbon-incarcerated iron/copper bimetallic nanoparticle (NP) catalysts prepared from nitrogen-containing polymers were developed. These catalysts showed activity higher than that of the corresponding monometallic NPs for aerobic ammoxidation of alcohols to nitriles. The important procedure for high activity in the catalyst preparation was found to be a simultaneous reduction of two metal salts.

Fe-based N-doped dendritic catalysts for catalytic ammoxidation of aromatic aldehydes to aromatic nitriles

Non-noble-metal-based catalysts for catalyzing the oxidative coupling of aldehydes and ammonia represent an efficient atom-economical synthetic route to produce nitriles. In this study, an effective Fe-modified N-doped carbon catalyst anchored on fibrous silica nanospheres (Fe-N/KCC-1-T) was successfully prepared by a facile strategy. 1,10-Phenanthroline with a strong chelating ability ensured the homogeneous, ultrafine distribution of Fe-based active sites, and the KCC-1 support material effectively enhanced the accessibility to these active sites, which corresponded to center-radial pore channels and a high surface area. As-fabricated Fe-N/KCC-1-T exhibited excellent catalytic performance for the ammoxidation of aldehydes under mild reaction conditions. A series of functionalized aldehydes were efficiently oxidized into the corresponding nitriles by using air as the green oxidant. Moreover, the catalyst was recycled for at least five runs without any clear decrease in the performance. Hence, this study is expected to provide an eco-friendly synthetic route to produce nitriles from easily available aldehydes and ammonia by using a cost-effective catalyst.

Enhanced Catalytic Performance Via Optimized Structural Properties for Dichlorotoluene Ammoxidation

A series of VO2 (B) nanostructures with different morphologies including nanobelts, urchins, and carambolas were hydrothermally synthesized and explored as catalyst precursors for ammoxidation of dichlorotoluene to optimize the structural properties. The catalytic results show the performance decreases in the following order: nanobelts> urchins> carambolas. On this basis, Cr doped VO2 (B) nanobelts were prepared and showed the yields of 2,6-dichlorobenzonitrle reaching up to 71.5%. This study provides valuable guidance on the design and development of highly effective ammoxidation catalysts.

Improvement of the conventional preparation methods in Co/BEA zeolites: Characterization and ethane ammoxidation

Ethane ammoxidation into acetonitrile (AN) was successfully catalyzed by Co/BEA solids issued from improved preparation methods. The catalyst issued from the impregnation of [Co(NH3)6]2+ complex into BEA zeolite is very active in ethane ammoxidation (48% of ethane conversion and 90% of selectivity towards AN at 450 °C). Over this solid, the combustion of hydrocarbon molecules into CO2 was inhibited since the inefficient oxidic species occupied hidden sites inside the zeolite host as demonstrated by the CO-TPR experiments. However, the exchange of [Co(OH2)6]2+ complex, accompanying the conventional impregnation and solid-state ion exchange, favoured the formation of Co3O4 oxide species, which restricted the ethane conversion into AN during ammoxidation. Nevertheless, the exchange of aqua complex in ammonia stream inhibited the formation of oxidic species and led to efficient ammoxidation catalysts. Meanwhile, ammonia favoured the formation of Co4N (detected by XRD, TPR and TPD) to the detriment of bare Co2+ ions. In this context, very low amounts (∼0.05 mmol g−1) of bare Co2+ ions, sited in the β-sites, are sufficient to catalyze ammoxidation at 450 °C. However, beside their amount, the stability of these ions is a crucial parameter to be considered and studied by FTIR upon CO adsorption at −196 °C.

Influence of V/P Ratio on the Catalytic Performance of VPO/SiO2 Catalysts for Ammoxidation of Chloro-Substituted Toluenes

A series of vanadium phosphate oxide (VPO) catalysts supported on silica (VPO/SiO2) with various mole ratios of V/P (nV:nP=1:0.8-1:3) were prepared through impregnation method. The catalytic activity was evaluated by ammoxidation reactions of several kinds of chloro-substituted toluenes (CT) in a fixed-bed reactor. The catalyst presented the best performance when nV:nP is 1:1.6. The prepared catalysts were characterized by N2 adsorption, hydrogen temperature programmed reduction (TPR) and ammonia temperature programmed desorption (TPD) and etc. The results reveal that P can decrease the bonding energy of V=O and increase the mobility of lattice oxygen which was beneficial for the improvement of the catalysts, while too much P can greatly decrease the average oxidation number of V which leads to deactivation of the catalysts. The surface acidity of the VPO/SiO2 catalysts is affected by nV:nP and the catalyst had the highest surface acidity when nV:nP is 1:1.6. The selectivity of catalysts is proportional to the surface acidity when nV:nP is lower than 1:3.0.

Physicochemical and catalytic properties of over- and low-exchanged Mo‒ZSM-5 ammoxidation catalysts

A series of Mo/ZSM-5 catalysts prepared by solid-state ion exchange at different Mo/Al molar ratios were characterized and tested in ethane and ethylene ammoxidation into acetonitrile. It has been concluded that the low-exchanged solid (Mo/Al = 0.2) stabilized MoO3, [Mo2O7]2− and [Mo7O24]6− species. However, besides these species, the solids prepared at Mo/Al = 0.5 and 1.5 stabilized [MoO4]2−. Nevertheless, only MoO3 and [Mo2O7]2− species were stabilized at Mo/Al = 1. The study performed by diffuse reflectance spectroscopy allowed the determination of the molar fraction relative to each Mo specie and, therefore, the calculation of the turnover frequency values. The catalytic activities of the various solids have been classified by taking into consideration the inefficiency of Al2(MoO3)4 phase, which inhibits the diffusion of reactants molecules towards the active sites, and amorphous MoO3 which catalyzes the undesired hydrocarbons’ combustion. However, [MoO4]2‒ species are efficient in the oxidative dehydrogenation of C2H6 into C2H4, while dimeric species catalyze the ammoxidation.

Designing Multifunctionality into Single Phase and Multiphase Metal-Oxide-Selective Propylene Ammoxidation Catalysts

Multifunctionality is the hallmark of most modern commercial heterogeneous catalyst systems in use today, including those used for the selective ammoxidation of propylene to acrylonitrile. It is the quintessential principle underlying commercial catalyst design efforts since petrochemical process development is invariably driven by the need to reduce manufacturing costs. This is in large part achieved through new and improved catalysts that increase selectivity and productivity. In addition, the future feedstocks for chemical processes will be invariably more refractory than those currently in use (e.g., replacing alkenes with alkanes or using CO2), thus requiring a disparate combination of chemical functions in order to effect multiple chemical transformations with the fewest separate process steps. This review summarizes the key chemical phenomena behind achieving the successful integration of multiple functions into a mixed-metal-oxide-selective ammoxidation catalyst. An experiential and functional catalyst design model is presented that consists of one or both of the following components: (1) a mixed-metal-oxide–solid solution where the individual metal components serve separate and necessary functions in the reaction mechanism through their atomic level interaction in the context of a single crystallographic structure; (2) the required elemental components and their catalytic function existing in separate phases, where these phases are able to interact for the purposes of electron and lattice oxygen transfer through the formation of a structurally coherent interface (i.e., epitaxy) between the separate crystal structures. Examples are provided from the literature and explained in the context of this catalyst design model. The extension of the model concepts to the design of heterogeneous catalysts in general is also discussed.

Carboxylic acid-modified metal oxide catalyst for selectivity-tunable aerobic ammoxidation

Controlling the reaction selectivity of a heterobifunctional molecule is a fundamental challenge in many catalytic processes. Recent efforts to design chemoselective catalysts have focused on modifying the surface of metal nanoparticle materials having tunable properties. However, precise control over the surface properties of base-metal oxide catalysts remains a challenge. Here, we show that green modification of the surface with carboxylates can be used to tune the ammoxidation selectivity toward the desired products during the reaction of hydroxyaldehyde on manganese oxide catalysts. These modifications improve the selectivity for hydroxynitrile from 0 to 92% under identical reaction conditions. The product distribution of dinitrile and hydroxynitrile can be continuously tuned by adjusting the amount of carboxylate modifier. This property was attributed to the selective decrease in the hydroxyl adsorption affinity of the manganese oxides by the adsorbed carboxylate groups. The selectivity enhancement is not affected by the tail structure of the carboxylic acid.

Influence of polyoxometalate structure in ammoxidation of 2-methylpyrazine

Keggin, Wells-Dawson and Preyssler structured polyoxometalates (POMs) were synthesized by different methodologies. The POMs were used as catalysts for ammoxidation of 2-methylpyrazine. The structural properties of POMs were determined by XRD, SEM, DRIFT, DRUV-vis, H2-TPR, NH3-TPD and N2-physisorption. Preyssler POM sample showed highest 2-methylpyrazine conversion (69%) and 2-cyanopyrazine selectivity (98%) at 380°C. Superior performance of Preyssler POM could be attributed to its redox behavior and relatively strong acid sites. Large number of ammonium ions in the secondary structure of Preyssler POM could also enhance the transformation of oxygenated 2-methylpyrazine species into 2-cyanopyrazine. A correlation between the amount of ammonium content of POMs and their catalytic ammoxidation activity was obtained.