Prereforming of <Emphasis Type="Italic">n</Emphasis>-tetradecane over Ce-promoted 50 wt% Ni/MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst with high coke resistance

The effect of Ce-promotion on 50 wt% Ni-based catalysts during the prereforming of n-tetradecane and its optimum content were investigated. The Ni catalyst was synthesized by deposition–precipitation method. Next, various amounts of Ce (0–13 wt%) were loaded on the Ni catalyst by impregnation. The characteristics of the prepared catalysts were analyzed by XRD, H₂-TPR, BET, BJH, and H₂-chemisorption analyses. The prepared catalysts were tested under the prereforming conditions (temperature = 400 °C, GHSV = 3000 h^?1, and S/C = 3 and 4). The Ni catalyst was easily deactivated under the following conditions: temperature = 400 °C, GHSV = 3000 h^?1, and S/C = 4. The stability of all Ce-promoted Ni catalysts was improved as compared to that of the Ni catalyst. Among the Ce-promoted catalysts, 5 wt% Ce/50 wt% Ni/MgO–Al₂O₃ catalyst showed excellent stability even under the severe condition of S/C = 3. SEM, TEM, and TG analyses were performed in order to identify the main factor responsible for the rapid deactivation of the Ni catalyst. In the case of 0Ce/50Ni, Ni particles were encapsulated by many folds of coke and it was related to the rapid catalyst deactivation. However, after Ce promoted on the Ni catalyst, the thickness of the coke layers and the number of encapsulated Ni particles decreased and the deposited amount of coke on the catalyst also decreased.     

Deactivation and regeneration of the B2O3/TiO2-ZrO2 catalyst in the vapor phase Beckmann rearrangement of cyclohexanone oxime

The deactivation and regeneration of B₂O₃/TiO₂-ZrO₂ catalyst for the vapor phase Beckmann rearrangement of cyclohexanone oxime to -caprolactam were studied. The fresh, deactivated and regenerated catalysts were characterized by using adsorption of nitrogen, X-ray diffraction (XRD), thermogravimetry (TG) and NH₃-temperature-programmed desorption (NH₃-TPD) techniques. The crystal structure and pore size distribution of the catalyst were retained after reaction, but the number of acid sites decreased significantly. There was a relationship between the amount of coke deposited on the catalyst and the decline in catalytic activity. These results suggest that the coke deposition on the surface of catalyst is mainly responsible for the catalyst deactivation. The catalytic activity can be recovered completely after calcining the deactivated catalyst in air flow at 600 °C for 8 h.     

Characterization of LaRhO3 perovskites for dry (CO2) reforming of methane (DRM)

This work reports on the characterization of LaRhO₃ perovskite as a catalyst for dry reforming of methane. The catalyst was studied using CH₄-temperature programmed reduction (TPR), H₂-TPR, and temperature programmed surface reaction (TPSR), and the changes in the crystal structure of the catalyst due to these treatments were studied by X-ray diffraction (XRD). XRD pattern of the freshly calcined perovskites showed the formation of highly crystalline LaRhO₃ and La₂O₃ phases. H₂-TPR of the fresh calcined catalyst showed a shoulder at 342°C and a broad peak at 448°C, suggesting that the reduction of Rh in perovskite occurs in multiple steps. XRD pattern of the reduced catalyst suggests complete reduction of the LaRhO₃ phase and the formation of metallic Rh and minor amounts of La(OH)₃. The CH4-TPR data show qualitatively similar results as H₂-TPR, with a shoulder and a broad peak in the same temperature range. Following the H₂-TPR up to 950°C, the same batch of catalyst was oxidized by flowing 5 vol. % O₂/He up to 500°C and a second H₂-TPR (also up to 950°C) was conducted. This second H₂-TPR differed significantly from that of the fresh calcined catalyst. The single sharp peak at 163°C in the second H₂-TPR suggests a significant change in the catalyst, probably causedby the transformation of about 90 % of the perovskite into Rh/La₂O₃. This was confirmed by the XRD studies of the catalyst reduced after the oxidation at 500°C. TPSR of the dry reforming reaction on the fresh calcined catalyst showed CO and H₂ formation starting at 400°C, with complete consumption of the reactants at 650°C. The uneven consumption of reactants between 400°C and 650°C suggests that reactions other than DRM occur, including reverse water gas shift (RWGS) and the Boudouard reaction (BR), probably as a result of in-situ changes in the catalyst, consistent with the H₂-TPR results. TPSR, after a H₂-TPR up to 950°C, showed that the dry reforming reaction did not light off until 570°C, which is much higher temperature than the one observed using fresh calcined catalyst. This shows that the uniform sites produced during the 950°C H₂-TPR are catalytically less active than those of the fresh calcined catalyst, and that no significant side reactions such as RWGS or the Boudouard reaction occur. This suggests that reduction leads to the formation of a single type of sites which do not catalyze simultaneous side reactions.     

Oligomerization of endo-dicyclopentadiene using a mesoporous catalyst in a fixed-bed reactor

The oligomerization of endo-dicyclopentadiene (endo-DCPD) over a mesoporous catalyst in a continuous-flow reactor at elevated pressure was studied to produce tricyclopentadiene (TCPD) and tetracyclopentadiene (TeCPD). The mesoporous material prepared from zeolite beta (MMZ_Hβ) was utilized as a catalyst. In addition, this study focused on the catalytic performance of the regenerated catalyst in comparison with the fresh catalyst. The TCPD and TeCPD were continuously produced through DCPD oligomerization over the MMZ_Hβ catalyst in a fixed bed reactor. At early time-on-stream, the conversion of endo-DCPD, the yield of TCPD and TeCPD, and the isomerization selectivity of TCPD in the fixed bed reactor were comparable to those in the batch-type reactor. The yield of oligomer containing TCPD and TeCPD decreased drastically from 28.5 % at 3 h time-on-stream to 21.5 % at 12 h time-on-stream, indicating that the catalyst was significantly deactivated. The in situ calcination in air flow at 500 °C was found to be effective for the regeneration of the used MMZ_Hβ catalyst.     

Synthesis of Highly-Dispersed Ni/Mesoporous Silica via an Ammonia Evaporation Method for Dry Reforming of Methane: Effect of the Ni Loadings

Mesoporous silica was used in conjunction with the ammonia evaporation method to prepare highly dispersed Ni catalysts for the dry reforming of methane (DRM). The effect of Ni dispersion on the catalytic performance was investigated by applying different Ni loadings. The pore structure, morphology, Ni dispersion, catalytic activity for DRM as well as the coke resistance were investigated. During the reaction at a relatively low temperature of 600 °C, all the three catalysts exhibited high stability in CH₄ and CO₂ conversion and excellent coke resistance, in comparison to Ni/SiO₂ catalyst prepared by the incipient wetness method. Among them, 10% Ni–SiO₂ exhibited the best catalytic performance with the maximum steady conversions of 62% and 69% for CH₄ and CO₂ at 600 °C, which was beneficial from its optimal Ni content and the presence of highly-dispersed metal nanoparticles confined in the mesopores.

     

Syngas production from ethanol dry reforming over Rh/CeO2 catalyst

Carbon dioxide reforming of ethanol over Rh/CeO₂ catalyst was deeply investigated at different reaction temperatures of 450–700 °C and reactant ratios (CO₂/ethanol from 1 to 3) under atmospheric pressure. The obtained results indicated that Rh/CeO₂ catalyst presented a promising activity and stability for syngas production from renewable bio-ethanol instead of conventional methane. Typically, CO₂-rich conditions (CO₂/ethanol = 3) were favorable for reaction process and dynamic coke cleaning, which led to remarkably stable performance over 65 h on stream. The strong redox capacity of CeO₂ support might also accelerate CO₂ activation and prevent the carbon accumulation over the catalyst surface. Additionally, tunable H₂/CO ratios were available by changing the CO₂/ethanol ratios. The results from characterization of samples before and after catalytic tests allowed to establish the relationship between textural properties and catalytic performance.     

From CH4 reforming with CO2 to pyrolysis over a platinum catalyst

At temperatures up to 1100°C, CH₄ and CO₂ react over a Pt wire to give mainly the reforming product CO, even at a CH₄/CO₂ ratio of 4.3. But if coke is present on the wire, the dominant reaction becomes the pyrolysis of CH₄ to form mainly C₂H₂ and C₆H₆. Thus, surface carbon poisons the reforming reaction and is autocatalytic for CH₄ pyrolysis. Higher temperatures and larger CH₄/O₂ ratios favor the formation of coke and the pyrolysis reaction. Molecular oxygen and, to a lesser extent, water have the opposite effect.     

Catalytic pyrolysis of HDPE in continuous mode over zeolite catalysts in a conical spouted bed reactor

A study has been carried out using HZSM-5, HY and Hβ zeolite-based catalysts in the pyrolysis of high density polyethylene (HDPE) continuously fed into a conical spouted bed reactor (CSBR) at 500 °C and atmospheric pressure, with the aim being to assess the yields and composition of the main products (both light olefins and automotive fuel hydrocarbons). Product streams have been grouped into seven lumps: light olefins (C₂–C₄) and light alkanes (<C₄) in the gas fraction, the liquid fraction consisting of three lumps (non-aromatic C₅–C₁₁ compounds, single-ring aromatics and C₁₁₊ hydrocarbons), wax and coke. The results are compared with those already obtained in thermal pyrolysis in a CSBR and with those obtained in the literature using catalysts in bubbling fluidized beds. HZSM-5 zeolite-based catalyst is very selective to light olefins, ≈58 wt% once equilibrated; whereas high yields of non-aromatic C₅–C₁₁ products (around 45 wt%) are obtained with Hβ and HY zeolite-based catalysts. Wax yield increases as reactions proceed, especially with HY and Hβ zeolite-based catalysts, due to catalyst deactivation by coke formation. Product distribution with the different catalysts and their evolution throughout continuous operation by feeding HDPE is explained according to the different properties of the zeolites used.     

Removal of carbonyl sulfide from CO2 stream using AgNO3-modified NaZSM-5

Removal of carbonyl sulfide (COS) from CO₂ stream is significant for the production and utilization of food grade CO₂. This study investigates the adsorption performance of Ag/NaZSM-5 as adsorbent prepared by incipient wetness impregnation for the removal of COS from a CO₂ stream in a fixed-bed adsorption apparatus. Effects of various conditions on the preparation of adsorbent, adsorption and desorption were intensively examined. The results revealed that COS can be removed to below 1×10^?9 from a CO₂ stream (1000 ppm COS/CO₂) using Ag/NaZSM-5 (10 wt% AgNO₃) with an adsorption capacity of 12.86 mg-g^?1. The adsorbent can be fully regenerated using hot air at 450 °C. The adsorption ability remained stable even after eight cycles of regeneration.     

Synthesis of Cu-Ce0.8Zr0.2O2 catalyst by ball milling for CO2 reforming of ethanol

A Cu-Ce_0.8Zr_0.2O₂ (Cu-CeZr) catalyst was synthesized by a facile ball-milling technique and its performance towards to CO₂ reforming of ethanol was deeply studied. Noticeably, syngas production from ethanol dry reforming is regarded as one of the efficient routes to minify the undesirable CO₂ discharge. Various characterization and detailed experimental tests were conducted to probe the influence of catalyst preparation method. Hence, the as-prepared Cu-CeZr sample presented a better activity compared with Cu/CeZr prepared by precipitation method. Full ethanol conversion was achieved at as low as 550?°C under the conditions where only 49?mol% H₂, 41?mol% CO and 10?mol% CH₄ were formed as main products. Additionally, Cu-CeZr catalyst exhibited satisfactory stability even under severe stoichiometric feed composition (ethanol/CO₂?=?1) during 90?h on-stream aging tests. Herein, the remarkably superior catalytic performance of Cu-CeZr was interpreted in terms of the improved Cu dispersion and the intimated metal-support interaction. This might shed light on syngas production from an sustainable process instead of conventional methane dry reforming.     

Reforming of CH4 with CO2 over Rh/H-Beta:Effect of Rhodium Dispersion on the Catalytic Activity and Coke Resistance

The effect of Rh dispersion on reforming of CH₄ with CO₂ over H‐Beta supported Rh catalysts has been investigated. The CH₄ and CO₂ conversion over the catalysts increase with increasing Rh loading from 0.5 wt% to 4.0 wt% in the reaction temperature range of 823–1123 K. The high TOF of CH₄ over 0.5 wt% and 1.0 wt% Rh/H‐beta may be attributed to high dispersion of rhodium species. The catalysts before and after the reaction were characterized by XRD, TEM, and TG‐DTA and the results indicate the catalysts with Rh loading of 0.5 wt% and 1.0 wt% exhibiting high resistance to coke. Under controllable conditions, we confirm that the coke is originated from methane dissociation and can be substantially oxidized by active oxygen species dissociated from the adsorbed carbon dioxide on the catalyst with high dispersion of Rh species.     

The Catalytic Dehydrogenation of c2h6 to c2h4 under non-Oxidative Conditions over the 6cr/g-al2o3Catalyst

In the present paper, the catalytic dehydrogenation of C₂H₆ to C₂H₄ under non-oxidative conditions was investigated in a fixed-bed micro-reactor under ambient pressure at 823 - 923 K. The 6Cr/g-Al₂O₃ catalyst was found to be the best catalyst among the g-Al₂O₃, SiO₂, MCM41, MgO and Si-2 supported chromium oxide catalysts. The features of the 6Cr/g-Al₂O₃ catalyst for the reaction could be listed as follows: (1) At 823 - 923 K, the C₂H₄ selectivity of 92.5-78.6% at a C₂H₆ conversion of 9.5-29.8% could be obtained. (2) The catalyst had the good regeneration performance, i.e., could be regenerated by air repeatedly. (3) The main products were C₂H₄, CH₄, H₂ and coke. No carbon oxides were identified.     

Effects of calcination and activation temperature on dry reforming catalysts

The effect of calcination temperatures on dry reforming catalysts supported on high surface area alumina Ni/γ-Al₂O₃ (SA-6175) was studied experimentally. In this study, the prepared catalyst was tested in a micro tubular reactor using temperature ranges of 500, 600, 700 and 800 °C at atmospheric pressure, using a total flow rate of 33 ml/min consisting of 3 ml/min of N₂, 15 ml/min of CO₂ and 15 ml/min of CH₄. The calcination was carried out in the range of 500–900 °C. The catalyst is activated inside the reactor at 500–800 °C using hydrogen gas. It was observed that calcination enhances catalyst activity which increases as calcination and reaction temperatures were increased. The highest conversion was obtained at 800 °C reaction temperature by using catalyst calcined at 900 °C and activation at 700 °C. The catalyst characterization conducted supported the observed experimental results.     

Efficient transfer hydrogenation of alkyl levulinates to γ-valerolactone catalyzed by simple Zr–TiO2 metal oxide systems

Zr–TiO₂ synthesized heterogeneous catalysts could efficiently convert ethyl levulinates (ELs) to γ-valerolactone (GVL) using isopropanol (2-PrOH) as H-donor. Obtained catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Scanning electron microscope (SEM), High revolution transmission electron microscope (HR-TEM), Fourier transform infrared spectroscopy (FT-IR), inductively coupled plasma optical emission spectroscopy (ICP-OES), NH₃/CO₂ temperature programmed desorption (NH₃/CO₂-TPD), pyridine-infrared spectroscopy, H₂ temperature-programmed reduction (H₂-TPR), and N₂ adsorption and desorption measurements. In total, 10 wt% Zr–TiO₂ with average nanoparticle sizes (ca. 4–6 nm) exhibited optimum catalytic activity after optimization of reaction temperature, reaction time, catalyst loading, as well as solvent effect. GVL yield reached 74% with 79% EL conversion at 190 °C for 5 h over 10 wt% Zr–TiO₂ in 2-PrOH. The high catalytic activity could be attributed to an appropriate proportion of acidic/basic sites, high Brønted/Lewis acid ratio, and large surface areas. Both acidic and basic sites lead to a synergistic effect on the concurrent activation of H-donor and substrate. The major side product ethyl 4-hydroxypentanoate (EHP) and other byproducts were found. GVL yield achieved from methyl levulinate (ML) and levulinic acid (LA) were 65% and 20%, respectively. Catalyst deactivation was observed due to coke deposits on the catalyst’s surface. The spent catalyst proved to be reusable to recover almost completely its initial activity after calcination (300 °C, 2 h). A plausible reaction mechanism is presented on the basis of characterization results.     

Low Temperature Diesel Particulate Filter Regeneration by Atmospheric Air Non-thermal Plasma Injection System

An experimental study of the regeneration of diesel particulate filter (DPF) was conducted through the use of a self-designed Non-thermal plasma (NTP) injection system with an experimental temperature of 20–300 °C, with atmospheric air being used as the gas source. The results revealed that the PM could be broken down into CO and CO₂ by NTP, through a discharge reaction of the NTP reactor. As the temperature increases, the mass of C₁ (mass of C in CO) showed an overall declining trend. Interestingly, the mass of C₂ (mass of C in CO₂) and C₁₂ (the sum of C₁ and C₂) both showed an initial increase, followed by a decrease. The peak mass of C₁₂ appears at 150 °C, and both axial and radial temperature gradients are less than the limit of DPF temperature gradient at this temperature. In conclusion, DPF can be regenerated by the NTP technology at a lower temperature, which can aid in the avoidance of thermal damage of DPF. The technology boasts a great advantage in adopting atmospheric air as its gas source, which can not only reduce costs, but also is convenient.     

Large Zeolite H‐ZSM‐5 Crystals as Models for the Methanol‐to‐Hydrocarbons Process: Bridging the Gap between Single‐Particle Examination and Bulk Catalyst Analysis

The catalytic, deactivation, and regeneration characteristics of large coffin‐shaped H‐ZSM‐5 crystals were investigated during the methanol‐to‐hydrocarbons (MTH) reaction at 350 and 500 °C. Online gas‐phase effluent analysis and examination of retained material thereof were used to explore the bulk properties of large coffin‐shaped zeolite H‐ZSM‐5 crystals in a fixed‐bed reactor to introduce them as model catalysts for the MTH reaction. These findings were related to observations made at the individual particle level by using polarization‐dependent UV‐visible microspectroscopy and mass spectrometric techniques after reaction in an in situ microspectroscopy reaction cell. Excellent agreement between the spectroscopic measurements and the analysis of hydrocarbon deposits by means of retained hydrocarbon analysis and time‐of‐flight secondary‐ion mass spectrometry of spent catalyst materials was observed. The obtained data reveal a shift towards more condensed coke deposits on the outer zeolite surface at higher reaction temperatures. Zeolites in the fixed‐bed reactor setup underwent more coke deposition than those reacted in the in situ microspectroscopy reaction cell. Regeneration studies of the large zeolite crystals were performed by oxidation in O₂/inert gas mixtures at 550 °C. UV‐visible microspectroscopic measurements using the oligomerization of styrene derivatives as probe reaction indicated that the fraction of strong acid sites decreased during regeneration. This change was accompanied by a slight decrease in the initial conversion obtained after regeneration. H‐ZSM‐5 deactivated more rapidly at higher reaction temperature.     

Properties and deactivation of the active sites of an MoZSM-5 catalyst for methane dehydroaromatization: Electron microscopic and EPR studies

The MoZSM-5 (4.0 wt % Mo) catalyst has been characterized by high-resolution transmission electron microscopy, EDXA, and EPR. Two types of molybdenum-containing particles are stabilized in the catalyst in the course of nonoxidative methane conversion at 750°C. These are 2-to 10-nm molybdenum carbide particles on the zeolite surface and clusters smaller than 1 nm in zeolite channels. According to EPR data, these clusters contain the oxidized molybdenum form Mo⁵⁺. The surface Mo₂C particles are deactivated at the early stages of the reaction because of graphite condensation on their surface. Methane is mainly activated on oxidized molybdenum clusters located in the open molecular pores of the zeolite. The catalyst is deactivated after the 420-min-long operation because of coke buildup on the zeolite surface and in the zeolite pores.     

Selective Coke Combustion by Oxygen Pulsing During Mo/ZSM‐5‐Catalyzed Methane Dehydroaromatization

Non‐oxidative methane dehydroaromatization is a promising reaction to directly convert natural gas into aromatic hydrocarbons and hydrogen. Commercialization of this technology is hampered by rapid catalyst deactivation because of coking. A novel approach is presented involving selective oxidation of coke during methane dehydroaromatization at 700 °C. Periodic pulsing of oxygen into the methane feed results in substantially higher cumulative product yield with synthesis gas; a H₂/CO ratio close to two is the main side‐product of coke combustion. Using ¹³C isotope labeling of methane it is demonstrated that oxygen predominantly reacts with molybdenum carbide species. The resulting molybdenum oxides catalyze coke oxidation. Less than one‐fifth of the available oxygen reacts with gaseous methane. Combined with periodic regeneration at 550 °C, this strategy is a significant step forward, towards a process for converting methane into liquid hydrocarbons.     

Ni/HZSM-5的结构及催化木糖醇水相加氢合成液体烷烃的性能研究

采用浸渍法制备了Ni/HZSM-5双功能催化剂,采用BET、XRD、NH3-TPD、H2-TPR、FTIR和TG等方法表征了催化剂比表面、孔结构、酸性、还原能力及骨架结构等信息,研究了其催化木糖醇水相加氢合成液体烷烃的性能及催化剂失活的原因。结果表明,在优化的金属中心/酸中心的协同作用下,木糖醇可通过水相加氢高选择性地合成C5-C6烷烃;过高的金属中心或酸中心均会导致C-C键断裂形成轻质烷烃,以2%Ni/HZSM-5催化剂上木糖醇水相加氢活性最高,木糖醇C转化率为94%液体烷烃总收率可达90%,这与其具有较大的比表面积、合适的孔径分布、较多的金属活性中心、适中的酸量和强酸量有关。催化剂6次重复使用后活性明显降低,其骨架部分脱铝和表面积碳是其失活的主要原因。     

Sorption-enhanced steam methane reforming over Ni/Al2O3/KNaTiO3 bifunctional material

The performance of a new lab-made bifunctional material Ni/Al₂O₃/KNaTiO₃ for producing high purity H₂ via sorption-enhanced steam methane reforming (SESMR) was investigated. A series of bifunctional materials with 10 wt% Ni loading but different wt% ratios of KNaTiO₃ and Al₂O₃ was prepared by wetness impregnation method. All the materials were calcined at 700 °C for 3 hours and screened for their catalytic activity in a continuous flow fixed-bed reactor. The material containing 50 wt% each of KNaTiO₃ and Al₂O₃ (designated as HM) was found to be the best choice. The optimum process parameters for the production of high purity H₂ were determined: temperature = 700 °C, steam to carbon (S/C) molar ratio = 6 and gas-hourly space velocity (GHSV) = 2000 cm³ g^-1 h^-1. The values of CH₄ conversion, H₂ yield and H₂ purity were 87, 87 and 90%, respectively, at the optimum reaction conditions. The adsorption capacity of HM was found to be 14.7 wt%. With a breakthrough time of 10 min, the material was stable for 8 adsorption-desorption cycles. The regeneration of HM was achieved with N₂ gas at the same reaction temperature. Overall, the activity of this material for SESMR was very promising.