Phthalic Anhydride fromo-Xylene Catalysis: Science and Engineering

Phthalic anhydride (PA): a valuable substrate in organic transformations

This review has been centralized on applications of phthalic anhydride (PA) as a valuable and significant heterocyclic substrate in two- and multicomponent organic reactions. The article has been subdivided into the following parts: (i) PA introduction by focusing on its characterization, synthesizing procedure, and multiple-aspect applications. In addition, the previous review articles based on PA have also been indicated; (ii) the applications of PA as a substrate have been subdivided into parts with a glance on the reaction components numbers; (iii) the applications of PA in esterification reactions; and (iv) some examples of PA in multistep synthesis. The review covers the corresponding literature up to the end of 2022. According to the abovementioned classifications, PA is a potent substrate to design a wide range of heterocyclic compounds that possess various kinds of properties and applications in chemistry, industry, and pharmaceuticals.

Chemical characterization and source attribution of organic pollutants in industrial wastewaters from a Chinese chemical industrial park

Accelerated urbanization and industrialization have led to an alarming increase in the generation of wastewater with complex chemical contents. Industrial wastewaters are often a primary source of water contamination. The chemical characterization of different industrial wastewater types is an essential task to interpret the chemical fingerprints of wastewater to identify pollution sources and develop efficient water treatment strategies. In this study, we conduct a non-target chemical analysis for the source characterization of different industrial wastewater samples collected from a chemical industrial park (CIP) located in southeast China. The chemical screening identified volatile and semi-volatile organic compounds that included dibutyl phthalate at a maximum concentration of 13.4 μg/L and phthalic anhydride at 35.9 μg/L. Persistent, mobile, and toxic (PMT) substances among the detected organic compounds were identified and prioritized as high-concern contaminants given their impact on drinking water resources. Moreover, a source analysis of the wastewater collected from the wastewater outlet station indicated that the dye production industry contributed the largest quantities of toxic contaminates (62.6%), and this result was consistent with the ordinary least squares and heatmap results. Thus, our study utilized a combined approach of a non-target chemical analysis, a pollution source identification method, and a PMT assessment of different industrial wastewater samples collected from the CIP. The results of the chemical fingerprints of different industrial wastewater types as well as the results of the PMT assessment benefit risk-based wastewater management and source reduction strategies.

Unravelling the redox mechanism and kinetics of a highly active and selective Ni-based material for the oxidative dehydrogenation of ethane

Bridging the gap between catalysis and reaction engineering during the kinetic analysis of the oxidative dehydrogenation of ethane over a highly active and selective Ni-based material.

Proton-Detected Multidimensional Solid-State NMR Enables Precise Characterization of Vanadium Surface Species at Natural Abundance

Heterogeneous catalysts fulfill vital roles in industrial processes; however, the nature of the catalytic surfaces, typically either containing a low abundance of active sites or being amorphous in nature, leads to difficulties when attempting to study the structure of the active sites. In this work, we show how making use of fast MAS ssNMR allows one to efficiently detect well-resolved ¹H-detected spectra of heterogeneous catalysts. This approach was applied to study the structure of surface species resulting from the grafting of VO(OⁱPr)₃ onto a partially dehydroxylated silica using the surface organometallic chemistry approach. The use of ¹H sensitivity enabled detection of various hetero- and homonuclear correlation spectra in order to study the structure of this system and to resolve the structure of the grafted vanadium complex. More specifically, VO(OⁱPr)₃ grafts through both protonolysis and opening of siloxane bridges to generate a bis-grafted species.

Deactivation of Commercial, High-Load o-Xylene Feed VOx/TiO2 Phthalic Anhydride Catalyst by Unusual Over-Reduction

An unusual temporal behavior of the by-product spectrum, as well as the temperature profiles of a commercial phthalic anhydride reactor, indicated a non-typical change of the incumbent catalyst. In order to understand these observations, catalyst samples were taken from this reactor and analyzed by standard physico-chemical methods. Catalyst samples from another commercial reference reactor with most similar operating conditions and catalyst lifetime were also taken for comparison. The detailed physical analysis did not indicate unusual thermal stress leading to catalyst deactivation by rutilisation or sintering of the titania phase. The chemical analysis did not reveal significant amounts of any of the known catalyst poisons, which would also contribute to an untypical catalyst deactivation/behavior. Quantitative X-ray diffraction measurements on the other hand revealed an unusually high degree of reduction of the vanadium species in the final polishing catalyst layer. Such an abnormal degree of catalyst reduction, and hence, irreversible damaging, was concluded to likely originate from a unit shutdown without sufficient air purging of the catalyst bed. Combustion analysis of the deactivated catalyst confirmed unusually high carbon contents in the finishing catalyst bed (L4) accompanied with a significant loss in the specific surface area by plugging the catalyst pores with high-molecular carbon deposits. According to the well-known Mars–van-Krevelen-mechanism, o-xylene and reaction intermediates remain adsorbed on the catalyst surface in case of a shutdown without air purging and will continue to consume lattice oxygen, accordingly reducing the catalytic species. This systematic investigation of used catalyst samples demonstrated the importance of sufficient air purging during and after a unit shutdown to avoid abnormal, irreversible damage and thus negative impact to catalyst performance.

Pathways, mechanisms, and kinetics: a strategy to examine byproduct selectivity in partial oxidation catalytic transformations on reducible oxides

We review experimental practices, common reaction pathways, and kinetic modeling strategies effective in understanding partial oxidation catalysis over reducible oxides.

Low temperature oxidation of o-xylene with hydrogen peroxide in the presence of vanadium xerogels

The present work is dedicated to investigation of vanadium xerogels deposited on titanium oxide for the oxidation process of o-xylene by hydrogen peroxide under the mild conditions. The structure of deposited vanadium catalyst and sizes of vanadium xerogels nanoparticles were investigated by physicochemical methods. The nano-sized particles (5-8 nm) of xerogel vanadium deposited on titanium oxide exhibit high catalytic activity in the decomposition of hydrogen peroxide and in the oxidation of o-xylene by hydrogen peroxide under mild conditions.

A new electrocatalytic systems based on bisorbents from rice husk

The article studies the synthesis of carbon-based and amorphous silicon dioxide bisorbents. Sorption characteristics of new bases for producing modified systems to use them in electrocatalysis are presented. For preparation of SiO2/C baseas rice husk (RH) was chosen as the raw material. A series of experiments was performed to optimize parameters of the RH carbonization by varying temperature and time of the process. The material obtained from the RH thermal destruction products was modified by the heteropoly compound (NH4)3[Co3O6Mo6O18H6] · nH2O and thermally reduced by hydrogen. The registration of the voltammetric curves was carried out at pH = 6.22 in the background electrolyte of 0.1 M Na2SO4 and pH = 4.45 in 0.1 M KC8H5O4.The potential ranges were -1.2В – 1.2 V and -1.0 V – 0.2 respectively. The mechanism of the electrochemical processes on these materials has been studied. It is shown that the obtained composite electrode materials exhibit electrochemical activity in the investigated potential regions, and they are characterized by the stability of redox properties. The main ways of using the obtained composites are outlined.

Self-assembled hierarchically structured organic-inorganic composite systems

Designing bio-inspired, multifunctional organic-inorganic composite materials is one of the most popular current research objectives. Due to the high complexity of biocomposite structures found in nacre and bone, for example, a one-pot scalable and versatile synthesis approach addressing structural key features of biominerals and affording bio-inspired, multifunctional organic-inorganic composites with advanced physical properties is highly challenging. This article reviews recent progress in synthesizing organic-inorganic composite materials via various self-assembly techniques and in this context highlights a recently developed bio-inspired synthesis concept for the fabrication of hierarchically structured, organic-inorganic composite materials. This one-step self-organization concept based on simultaneous liquid crystal formation of anisotropic inorganic nanoparticles and a functional liquid crystalline polymer turned out to be simple, fast, scalable and versatile, leading to various (multi-)functional composite materials, which exhibit hierarchical structuring over several length scales. Consequently, this synthesis approach is relevant for further progress and scientific breakthrough in the research field of bio-inspired and biomimetic materials.

Hierarchically structured vanadium pentoxide-polymer hybrid materials

Biomimetic composite materials consisting of vanadium pentoxide (V2O5) and a liquid crystal (LC) "gluing" polymer were manufactured exhibiting six structural levels of hierarchy, formed through LC phases. The organic matrix was a polyoxazoline with pendant cholesteryl and carboxyl units, forming a lyotropic phase with the same structural orientation extending up to hundreds of micrometers upon shearing, and binding to V2O5 via hydrogen bridges. Composites consisting of V2O5-LC polymer hybrid fibers with a pronounced layered structuring were obtained. The V2O5-LC polymer hybrid fibers consist of aligned V2O5 ribbons, composed of self-assembled V2O5 sheets, encasing a chiral nematic polymer matrix. The structures of the V2O5-LC polymer composites strongly depend on the preparation method, i.e., the phase-transfer method from aqueous to organic medium, in which the polymer forms LC phases. Notably, highly defined micro- and nanostructures were obtained when initiating the synthesis using V2O5 tactoids with preoriented nanoparticle building units, even when using isotropic V2O5 dispersions. Shear-induced hierarchical structuring of the composites was observed, as characterized from the millimeter and micrometer down to the nanometer length scales using complementary optical and electron microscopy, SAXS, μCT, and mechanical nanoindentation.

Selective oxidation of o-xylene to phthalic anhydride: from conventional catalysts and technologies toward innovative approaches

This paper discusses the gas-phase selective oxidation of o-xylene to phthalic anhydride, one of the chemical processes most studied in the 1980s and 90s. Specifically, it is our aim to examine some aspects which may offer ideas for the development of more innovative reactor technologies or catalyst formulations, and to discuss some peculiarities of this process and of the V/Ti/O catalysts that have been overlooked in the past.

Co and Mn polysiloxanes as unique initiator-catalyst-systems for the selective liquid phase oxidation of o-xylene

Co and Mn polysiloxanes are unique catalyst/initiator systems for the liquid phase oxidation of o-xylene showing higher activity than Co naphthenates, which is related to the weak interaction of the polar products with the hydrophobic surface as well as the absence of hydroxyl groups and surrounding oxygenates limiting radical quenching.

Mesocrystals of vanadium pentoxide: a comparative evaluation of three different pathways of mesocrystal synthesis from tactosol precursors

Vanadium pentoxide mesocrystals were synthesized from a mineral liquid crystalline precursor phase, a so-called tactosol. For comparative evaluation of solid formation from that phase, the distance between the vanadium pentoxide particles was lowered by three different modes: (a) by adding a 0.1 M NaCl solution, the electric double layer was compressed and controlled particle aggregation was induced; (b) application of external pressure by ultracentrifugation resulted in particle compression and final crystallization; (c) an acrylic acid/sulfonic acid copolymer was added to introduce polymer-mediated particle alignment and densification. In all three cases, the preorientation of the particles within the liquid crystal remained, and different mesocrystals were formed. This was demonstrated by comparative analysis of the resulting structures by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and polarization microscopy.

Toward an Understanding of the Formation of Vanadia−Titania Catalysts

Structures of hydrated vanadia species on the TiO2-anatase surfaces were investigated using the semiempirical molecular orbital method MSINDO. The (101), (001), and (100) surfaces of anatase were considered. They were modeled by appropriate two-dimensional cyclic clusters of TiO2. Monomeric and dimeric hydrated vanadia species on the anatase surfaces were simulated by adsorbing VO4H3 and V2O7H4 molecules, respectively. Different adsorption structures were considered, and their stabilities at 300 and 600 K were tested by constant-temperature Born-Oppenheimer molecular dynamics simulations in the framework of MSINDO. Structural features of the vanadia-titania catalysts found in extended X-ray absorption fine structure, secondary ion mass spectrometry, IR, Raman, and NMR spectroscopy and conductivity experiments can be explained by the present calculations.