The study investigated the reduction behavior of oxide scale on hot-rolled high-strength steel through simulated annealing tests in 30% H2-N2 at 500 degrees C-1100 degrees C. The research delved into the kinetics of reduction, internal oxidation, and associated mechanisms. Findings revealed that at 500 degrees C and 600 degrees C, the reduction product was porous iron, transitioning to dense iron between 800 degrees C and 1100 degrees C. The shift from porous to dense structures occurred, with the slowest reduction rate observed at 700 degrees C. Internal oxidation, featuring silicon and manganese oxides, occurred from 800 degrees C to 1100 degrees C, with minimal depth changes despite increasing reduction temperatures. Equilibrium oxygen partial pressure at the oxide scale/substrate interface predominantly controlled internal oxidation, where oxygen atoms from oxide scale reduction drove the nucleation and growth of internal oxides. The reduction process involved hydrogen diffusion through the gas boundary layer, internal diffusion of hydrogen within solid products, chemical reactions at the outer gas/oxide scale interface, outward diffusion of water vapor, and the formation of internal oxides. Comparing the reduction rate progression to the reduced iron growth rate at the gas/oxide scale interface, key reduction products were identified as porous and dense iron.

Abstract Conventional industrial technologies for cyclohexanone production, a key precursor to ε-caprolactam, primarily cyclohexane oxidation (CHA-Ox) and cyclohexene hydration (CHE-Hydr), are constrained by an inherent trade-off between conversion and selectivity. This leads to low carbon atom utilization or high energy intensity, together with substantial environmental burdens. The cyclohexene esterification–reduction (CHE-ER) route, first proposed by the Research Institute of Petroleum Processing (RIPP), delivers exceptional conversion and selectivity and therefore offers a promising platform for next-generation cyclohexanone production. However, the central challenge has been to translate the intrinsic advantages of this chemistry into a process that is simultaneously economically competitive and environmentally sustainable. Here we report a set of critical chemical engineering innovations that streamline process design and substantially reduce energy consumption. By leveraging the inertness of cyclohexane during cyclohexene esterification, we designed a new extraction system that selectively separates benzene from its partial hydrogenation products. We further implemented a hybrid reactor configuration integrating a fixed-bed reactor with a catalytic reactive distillation reactor for cyclohexene esterification with acetic acid. In addition, we identified and strategically harnessed the beneficial roles of cyclohexane in facilitating reaction heat dissipation and excess acetic acid separation. These innovations have been successfully deployed in a 400 kt yr–1-capacity industrial plant for cyclohexanone production via the CHE-ER route, affording nearly complete cyclohexene conversion and cyclohexyl acetate selectivity above 99.0%. This work establishes a new-generation of industrial technology for cyclohexanone production that maximizes economic benefit, while minimizes energy demand and environmental impacts associated with conventional processes.

Hydrogen reduction of oxide scale, as an environmentally friendly technology, is required to replace the conventional acid pickling process and provides a promising green production route for hot-dip galvanizing. In order to understand the hydrogen reduction mechanism of oxide scale in advanced high strength steel, the cross-section morphology, Mn distribution, and decarburization have been studied with the reduction time of 1 similar to 10 min in a 5%H-2-N-2 atmosphere at 900 degrees C. Results show a clear relationship between the surface iron layer and the wavy reduction at the interface. The thickness of the surface iron layer remains almost unchanged throughout the whole reduction process, whereas the reduction at the oxide scale/steel interface plays a dominant role. Three points are proposed to explain the reasons for the rapid growth of reduced iron at the interface, dissolved carbon and internal oxidation consuming oxygen released from (Fe,Mn)(1-x)O decomposition, carbon reacting with water vapor, and microcracks acting as efficient rapid channels of gaseous products. Meanwhile, Mn moves upward along with (Fe,Mn)(1-x)O, due to the faster growth of interface reduced iron, which reveals Mn migration from the perspective of reduction evolution.

The influence of Al addition on ferritic stainless steel oxidation resistance has been investigated. Experiments are performed using a synthetic automotive exhaust gas at 950 degrees C and 1050 degrees C. In the case of 0Al steel, a double-layered oxide scale is observed at both temperatures. At 1050 degrees C, the oxide scale exhibits cracking due to thermal stress. Oxidizing atmosphere penetration results in Si enrichment at the oxide scale/substrate interface. Ultimately, multilayered Si-rich bands are formed sequentially in the oxide scale. In contrast, 0.7Al steel forms a protective Al2O3 layer at the oxide scale/substrate interface, and needle-shaped Al2O3 is formed under it due to volume shrinkage. Anion and cation diffusion are inhibited by the upper Al2O3 layer, preventing substrate corrosion. The findings of this work demonstrate a significant enhancement of oxidation resistance due to Al addition.

The oxidation behavior of SUS430 ferritic stainless steel is studied during isothermal oxidation at 1100 °C for 2 h under a mixture of 10, 30, and 50% water vapor and air, and oxidation kinetics curves are drawn. The surface morphology and phase composition of oxide scale are analyzed using X‐Ray diffractometer, scanning electron microscope, and energy dispersive spectrometer. The oxidation kinetic curves under three different humidities are S‐shaped and include three stages: induction period, acceleration period, and deceleration period. The controlling steps under 10% water vapor and air are nucleation and growth, while under 30% and 50% water vapor and air are both phase boundary control reactions. The induction period becomes shorter and the breakaway oxidation occurs earlier with increasing water vapor content. The structure of oxide scale produced is layered, with the outer layer being iron oxide and the inner layer being mainly the Fe–Cr spinel phase. The volatilization of Cr and the growth stress of the Cr 2 O 3 layer cause the formation of nodules, and a large number of cracks are generated in oxide scale. The cracks provide diffusion paths, accelerating the diffusion of Fe ions and electrons, as well as the erosion of the substrate.

The high-temperature oxidation behavior of 444 ferritic stainless steel has been studied in cyclic oxidation experiments using synthetic automotive exhaust gas atmospheres at 950 and 1050 degrees C. The weight gain per unit area of the 444 ferritic stainless steel following oxidation at 950 degrees C for 100 h iss 85.7% lower than recorded at 1050 degrees C. The oxide scale at both temperatures consisted of Fe-Cr and Mn-Cr spinels in the outer layer and Cr2O3 in the inner layer. Nodule formation and spallation of the oxide scale are identified as the main causes of breakaway oxidation. The depth of the internal oxides gradually increases with the oxidation time. The nucleation and growth of internal SiO2 result in the formation of metal protrusions, which are eventually consumed in the formation of a SiO2 layer. The SiO2 layer is formed at the interface between the oxide scale and the substrate at 1050 degrees C. The nucleation and growth of internal SiO2, in combination with lateral growth of SiO2 at the Cr2O3 layer/substrate interface contributed to the formation of the SiO2 layer.

The understanding of oxide scale reduction mechanisms after microstructure transformation under different preheating conditions is incomplete. Herein, the reduction kinetics and microstructure transformations of hot rolled steel strip oxide scale during reduction (30% H2–N2) annealing are studied in detail using thermogravimetric and microstructure analyses, and mathematical modeling based on the gas–solid reaction. The results show that the rate‐determining steps of the reduction reaction are nucleation and growth of new phase between 500 and 600 °C, and gas–solid interface reactions between 700 and 800 °C. Microstructure transformation of the oxide scale occurs during the preheating process: at 500 °C, the eutectoid iron preferentially dissolves, and short‐range diffusion of Fe ions into adjacent Fe3O4 increases their content in the metal oxide; at 600 °C, nucleation and growth of Fe1 − yO occur, and some Fe3O4 precipitates and white α‐Fe are found in the Fe1 − yO layer, whereas the majority of the Fe3O4/iron eutectoid structure is retained; between 700 and 800 °C, the oxide scale forms outer and inner layers of Fe3O4 and Fe1 − yO, respectively. After preheating and reduction, the reduced products are porous iron over 500–600 °C, while porous and dense iron occur at 700 °C; dense iron forms as whiskers or granules between 700 and 800 °C. The surface quality of hot rolled steel strip after reduction annealing is subsequently improved as surface cracks are infilled by the newly formed dense iron.

Using a thermogravimetric analyzer (TGA), Fe–10Cr steel was oxidized in dry air and in a mixed atmosphere of air and water vapor at a relative humidity of 50% and a temperature of 800–1200 °C for 1 h. The oxidation weight gain curves under the two atmospheres were drawn, the oxidation activation energy was calculated, and the phase and cross-sectional morphology of the iron oxide scales were analyzed and observed by X-ray diffractometry (XRD) and optical microscopy (OM). The results showed that when the oxidation temperature was 800 °C, the spheroidization of Fe–10Cr steel occurred, and the oxidation kinetics conformed to the linear law. At 900–1200 °C, the oxidation kinetics followed a linear law in the preliminary stage and a parabolic law in the middle and late stages. In an air atmosphere, when the oxidation temperature reached 1200 °C, Cr2O3 in the inner oxide layer was partially ruptured. In an atmosphere with a water vapor content of 50%, Cr2O3 at the interface reacted with H2O to generate volatile CrO2(OH)2, resulting in a large consumption of Cr at the interface. At the same time, a large number of voids and microcracks appeared in the iron oxide layer, which accelerated the entry of water molecules into the substrate, as well as the oxidation of Fe–10Cr steel, and caused the iron oxide scales to fall off. Due to the volatilization of Cr2O3 and the conversion from internal oxidation to external oxidation, the internal oxidation zone (IOZ) of Fe–10Cr steel under water vapor atmosphere decreased or even disappeared.

The microstructure transformation of oxide scale in hot‐rolled steel strips during the preheating process is studied by thermal simulation at temperatures ranging from 530 to 800 °C. The results show that the original structure of the oxide scale comprises an outer Fe3O4 layer, an inner Fe3O4/Fe eutectoid, and some precipitated Fe3O4. The Fe3O4/Fe eutectoid structure is first transformed into wüstite. After the eutectoid structure is completely transformed into wüstite, Fe3O4 precipitates are transformed into wüstite with aging. Then, white Fe is dissolved and diffused into wüstite to give a homogenous wüstite layer. The thickness of outer Fe3O4 layer decreases as the temperature increases, indicating that the outer Fe3O4 also transforms into wüstite. The heating rate and temperature are important parameters influencing the phase transformation of the oxide scale. More wüstite is formed at a slower heating rate and higher temperature; a larger number of pores are found inside the wüstite layer with increasing temperature; pores caused by transformation of the oxide scale are created by the density difference between wüstite and Fe3O4.

The atmospheric corrosion behavior of a hot-rolled strip with four types (I–IV) of oxide scale was investigated using the accelerated wet–dry cycle corrosion test. Corrosion resistance and porosity of oxide scale were studied by potentiometric polarization measurements. Characterization of samples after 80 cycles of the wet–dry corrosion test showed that scale comprised wüstite and magnetite had strongest corrosion resistance. Oxide scale composed of inner magnetite/iron (>70%) and an outer magnetite layer had the weakest corrosion resistance. The corrosion kinetics (weight gain) of each type of oxide scale followed an initial linear and then parabolic (at middle to late corrosion) relationship. This could be predicted by a simple kinetic model which showed good agreement with the experimental results. Analysis of the potentiometric polarization curves, obtained from oxide coated steel electrodes, revealed that the type I oxide scale had the highest porosity, and the corrosion mechanism resulted from the joint effects of electrochemical behavior and the porosity of the oxide scale. In the initial stage of corrosion, the corrosion product nucleated and an outer rust layer formed. As the thickness of outer rust layer increased, the corrosion product developed on the scale defects. An inner rust layer then formed in the localized pits as crack growth of the scale. This attacked the scale and expanded into the substrate during the later stage of corrosion. At this stage, the protective effect of the oxide scale was lost.

In the case of Fe–1Cr–0.2Si steel, tube furnace oxidation was carried out for 120 min and 30 min. These studies, along with the high-temperature oxidation behavior of Fe–1Cr–0.2Si steel, were examined from 700 to 1100 °C. It has been observed that with an increase in the oxidation time, the oxidation weight gain per unit area of Fe–1Cr–0.2Si steel changed from a linear to a parabolic relationship. The time was shortened when the oxidation phase was linear. When the oxidation temperature exceeded 900 °C, the value of WTransition decreased, and the oxidation rule changed. It could be considered that overall, the iron oxide structure of Fe–1Cr–0.2Si steel is divided into two layers. The formation of an outer oxide of iron is mainly caused by the outward diffusion of cation, while the inward diffusion of O ion forms the inner oxides of chromium and silicon. As the temperature increases, the thickness of the outer iron oxide gradually increases, and the thickness ratio of the inner mixed layers of chromium- and silicon-rich oxides decreases; however, the degree of enrichment of Cr and Si in the mixed layer increases. After high-temperature oxidation, Cr and Si did not form a composite oxide but were mechanically mixed in the form of FeCr2O4 and Fe2SiO4, and no significant delamination occurred.

A strategy based on galvanic replacement between metallic Zn and Ru salt followed by acid treatment was developed to fabricate supported Ru-Zn/ZrO2 nanocomposite catalysts with controlled contents of Zn for the benzene partial hydrogenation to cyclohexene. The catalysts were systematically characterized by techniques such as extended X-ray absorption fine structure, X-ray photoelectron spectroscopy, and transmission electron microscopy. In benzene partial hydrogenation, with the decrease in the content of Zn, the turnover frequency (TOF) of benzene increased monotonically, whereas the selectivity to cyclohexene evolved in a volcanic trend, passing through a maximum of 72%. Kinetic analysis indicated that with the depletion of Zn, the rate constant for benzene hydrogenation to cyclohexene and that for cyclohexene hydrogenation to cyclohexane increased simultaneously, but the extents of the increments were at variance. It was identified that the ratios of the rate constants were in parallel with the change in the selectivity to cyclohexene, which is attributed to the electronic effect of metallic Zn that modifies the interactions of Ru with benzene and cyclohexene.

We report the modification effects of Pd and Pt on the partial hydrogenation of benzene to cyclohexene over the Ru/ZrO2 catalyst. The Ru/ZrO2, Ru-Pd/ZrO2 and Ru-Pt/ZrO2 catalysts were prepared by the wetness impregnation-chemical reduction method at room temperature. The catalysts were characterized by N2 physisorption, H2 chemisorption, powder X-ray diffraction (XRD), ultraviolet-visible diffuse reflectance spectroscopy (UV-DRS), transmission electron microscopy (TEM), X-ray absorption spectroscopy (XAS), and differential scanning calorimetry (DSC). It was identified that the Ru-Pd and Ru-Pt alloys were formed on the Ru-Pd/ZrO2 and Ru-Pt/ZrO2 catalysts, which improved the coordination number of Ru. In the partial hydrogenation of benzene to cyclohexene, while the modification of the Ru/ZrO2 catalyst with Pd or Pt decreased the turnover frequency (TOF) of benzene, the initial selectivity ( S 0) to cyclohexene was improved. The Ru-Pd/ZrO2-0.2 and Ru-Pt/ZrO2-0.15 catalysts with the optimal Pd/Ru and Pt/Ru molar ratios of 0.2 and 0.15 exhibited similar S 0 and the yield of cyclohexene of about 77% and 44%, respectively. On the basis of the characterization results, the modification effects of Pd and Pt on the activity and selectivity of the Ru/ZrO2 catalyst were discussed.

Partial hydrogenation of benzene to cyclohexene is an important industrial process and features exceptional superiority to processes such as dehydration of cyclohexanol, dehydrogenation of cyclohexane, and the Birch reduction in terms of inexpensive feedstock, succinct reaction route and consequently, improved operational simplicity. In this work, the pore size effect on the partial hydrogenation of benzene to cyclohexene over the Ru-Zn/ZrO2 catalysts was studied for the first time. Three ZrO2 supports with the same tetragonal crystallographic form (t-ZrO2) but different pore sizes were synthesized by the precipitation and the solvothermal methods. Using these ZrO2 samples, the Ru-Zn/ZrO2 catalysts were prepared by the deposition-precipitation method followed by reduction in ZnSO4 center dot 7H(2)O aqueous solution. The supports and catalysts were characterized by powder X-ray diffraction (XRD), N-2 physisorption, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), CO chemisorption, X-ray photoelectron spectroscopy (XPS), X-ray absorption near-edge structure (XANES), temperature-programmed reduction of H-2 (H-2-TPR), and transmission electron microscopy (TEM). It is identified that the Ru nanoparticles (NPs) on these catalysts had similar size and chemical state. In the partial hydrogenation of benzene to cyclohexene, a pronounced pore size effect of the catalyst was identified. With the increase in the pore size, while the turnover frequency (TOF) of benzene was essentially unchanged, the initial selectivity (S-0) to cyclohexene increased steadily. The Ru-Zn/ZrO2(11.7) catalyst with the ZrO2 support having the pore size of 11.7 nm exhibited the highest So (88%) and yield (54%) of cyclohexene. On the basis of the characterization results, the similarity in the TOFs of benzene on the Ru-Zn/ZrO2 catalysts with different pore sizes is associated with the identical sizes of the Ru NPs. On the other hand, we tentatively propose that the ZrO2 support with large pore size is beneficial for the out-diffusion of the cyclohexene nano-droplets formed in the pore channels, thus avoiding consecutive hydrogenation to cyclohexane and improving the So.

After two decades’ endeavor, the Research Institute of Petroleum Processing (RIPP) has successfully developed a green caprolactam (CPL) production technology. This technology is based on the integration of titanium silicate (TS)-1 zeolite with the slurry-bed reactor for the ammoximation of cyclohexanone, the integration of silicalite-1 zeolite with the moving-bed reactor for the gas-phase rearrangement of cyclohexanone oxime, and the integration of an amorphous nickel (Ni) catalyst with the magnetically stabilized bed reactor for the purification of caprolactam. The world’s first industrial plant based on this green CPL production technology has been built and possesses a capacity of 200kt·a−1. Compared with existing technologies, the plant investment is pronouncedly reduced, and the nitrogen (N) atom utilization is drastically improved. The waste emission is reduced significantly; for example, no ammonium sulfate byproduct is produced. As a result, the price difference between CPL and benzene drops. In 2015, the capacity of the green CPL production technology reached 3 × 106 t·a−1, making China the world’s largest CPL producer, with a global market share exceeding 50%.

Metal-organic frameworks (MOFs) have attracted enormous research interests not only because of their merits such as high specific surface area, high porosity, and regular pore channels, but also due to their peculiarities of extremely abundant chemical and structural diversity and tunability. In this work, we synthesized MIL-53(Al) and MIL-53(Cr) containing one coordination metal and the novel MIL-53(AlxCr1)(x= 1, 2, 3, and 4) MOFs containing two coordination metals as the supports for the Ru-B/MIL-53 catalysts, which were prepared by the facile impregnation- chemical reduction method. In the challenging partial hydrogenation of benzene to cyclohexene, it is revealed that the Al/Cr ratio had pronounced influences on both the initial hydrogenation rate (r(0)) and the initial selectivity to cyclohexene (S-0). In general, MIL-53 containing a higher fraction of Al affords a higher r(0), while MIL-53 containing both Al and Cr is conducive to a higher S-0 than either MIL-53(Al) or MIL-53(Cr) containing only one coordination metal. On the Ru-B/MIL-53(Al3Cr1) catalyst exhibiting the highest selectivity to cyclohexene, the r(0) and S-0 were 9.2 mmol/(min.g) and 71%, respectively. The best Ru-B/MIL-53(Al3Cr1) catalyst and the Ru-B/MIL-53(Cr) catalyst displaying the lowest selectivity to cyclohexene were comparatively characterized to have an insight into the difference in their catalytic performance. It is found that while both catalysts had similar Ru/B molar ratio, electronic property, and microstructure, the Ru-B/MIL-53(Al3Cr1) catalyst had higher active surface area (Sact), smaller and more highly dispersed Ru-B nanoparticles (NPs), and stronger metal-support interaction than the Ru-B/MIL-53(Cr) catalyst. The smaller Ru-B NPs could not only provide more active sites for the hydrogenation of benzene, but also be beneficial to the formation of cyclohexene. By further optimization of the reaction conditions, at 180 degrees C, H-2 pressure of 5.0 MPa, and using 100 mu L of ethanolamine as the modifier, a cyclohexene yield of 29% was obtained over the Ru- B/ MIL- 53( Al3Cr1) catalyst.

The supported Ru catalysts were prepared by the impregnation-chemical reduction method to investigate the effect of some conventional oxide supports (SiO2, m-ZrO2, t-ZrO2,.-Al2O3, and P25) on the partial hydrogenation of toluene to methylcyclohexenes. The catalysts were characterized by N-2 physisorption, powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). It was found that the supports influenced the size of the Ru nanoparticles (NPs) and consequently the catalytic performance. With the increase in the size of the Ru NPs from 2.6 to 17.3 nm, the turnover frequency (TOF) of toluene and the initial selectivity (S-0) to methylcyclohexenes increased first, reached the maximum, and then decreased, following a volcano-like curve. At the Ru particle size of 3.0 nm, both TOF and S-0 reached the highest values. Reaction conditions, such as the type and concentration of the modifiers, the temperature, and the pressure, were optimized over the best Ru/P25 catalyst among the supported Ru catalysts investigated herein. Under the reaction conditions of 423 K, H-2 pressure of 5.0 MPa, and using 0.25 g zinc sulfate heptahydrate as the modifier, the initial hydrogenation activity (r(0)) of 26 mmol.g(-1) . min(-1), the S-0 of 57%, and the methylcyclohexenes yield of 36% were obtained.

Ru–B/MIL-53(AlCr) affords an exceptionally high turnover frequency (TOF) of 6.4 s−1for hydrogenation of benzene to cyclohexane under mild reaction conditions.

Site-specific deposition of metal nanoparticles (NPs) on metal oxide surfaces is challenging but of particular importance for the development of catalytic materials with improved or new performance. We report here that Ru NPs can be directed to the rutile/anatase junction of P25 TiO2 via a facile wetness impregnation-chemical reduction method at room temperature. In the partial hydrogenation of benzene to cyclohexene, the Ru/P25 catalyst outperformed the Ru NPs supported on phase-pure rutile and anatase as well as physically mixed Ru/rutile and Ru/anatase, both in activity and in selectivity. We identified a unique electron-deficient Ru species (Ru delta+) on the Ru/P25 catalyst originated from the Ru-O linkages connecting the Ru NPs with the rutile/anatase junction. This interfacial Ru delta+ species gave rise to an especially tightly bonding benzene species while lowering the adsorption strength of cyclohexene, thus granting the Ru/P25 catalyst superior activity and unprecedented selectivity toward cyclohexene (initial selectivity 90%). (C) 2015 Elsevier Inc. All rights reserved.