Catalysis Surveys from Asia最新文献

Fluidized Catalytic Cracking (FCC) is one of the key processes of any petroleum refinery as it produces gasoline, Liquefied Petroleum Gas (LPG) and valuable petrochemical feedstock viz. ethylene and propylene. FCC is a catalytic process where zeolite (USY and ZSM-5) based catalysts are being used, contain a high concentration of acidic sites, which are responsible for cracking heavy hydrocarbon molecules into smaller ones. During these cracking reactions, significant coke formation occurs over the catalyst surface and blocks the pores, thus resulting drop in catalytic activity. To regain the catalyst activity, the coke on the catalyst is burned in the FCC regenerator unit and provides heat demand for the FCC riser bed where the cracking reaction takes place and the cycle continues. The temperature of the FCC regenerator reaches around 700 °C due to the combustion of coke on the catalyst. Due to incomplete combustion of coke on catalyst produces CO which burns above the catalyst bed, which is denoted as a dilute bed. The heat of reaction of CO combustion needs to be realized on catalysts bed and also to avoid the heat loss in the regenerator dilute bed. Higher dilute bed temperature damages the FCC regenerator internals, which is to be avoided. Conventionally, additives named CO Combustion Promoters (COPs) have been used for the promotion of CO to CO₂ in the catalyst bed which helps in improving regeneration of FCC equilibrium catalysts. The present article covers the concept and various types of COP reported in the literature. Different preparation methodologies, physico-chemical properties and evaluation results have been discussed. These insights would be helpful to understand the structure–property–activity relationship of COP. Further, it can also help to select the right COP for the desired commercial applications.

Series of Ti/Cu-SSZ-13 zeolite catalysts with variable Ti content were prepared via convenient in-situ one-pot synthesizing strategy. Systematic evaluations of the NH₃-SCR catalytic performance over the obtained catalysts were conducted. Results show that Ti/Cu-SSZ-13 with appropriate Ti content (in the current work Ti_0.81/Cu_2.15-SSZ-13) could serve as capable candidate for NH₃-SCR application, as it exhibits highly efficient catalytic activity with expanded operation temperature window width from 140 to 540 °C, nearly 100% N₂ selectivity, as well as superior tolerability against water vapor and SO₂. Further structural/physicochemical characterizations demonstrate that the obtained Ti/Cu-SSZ-13 catalysts possess well-crystallized characteristic chabazite (CHA) structure. Isolated Cu²⁺ and monomeric Ti⁴⁺ are recognized as the primary active species, as the former mainly contributes to SCR reaction at low temperatures, while the latter are conducive for improving the high temperature SCR activity. Ti over doping would result in partial destruction of the zeolite structure, occupation of Cu²⁺ cation sites and formation of surface aggregated TiO_x, thus leading to unsatisfactory NH₃-SCR performances. Moreover, formation of agglomerated CuO_x species during hydrothermal ageing and blockage of surface active sites by sulfate species formed during SO₂ pretreatment are considered responsible for activity deterioration in the tolerability tests.

Iridium nanoparticles were synthesized between graphite layers by thermal treatment of the mixture of iridium chloride (IV) and graphite powder under chlorine atmosphere followed by hydrogen reduction (Ir-GIC). In Ir-GIC samples with 1–6 wt% iridium metal loadings, all iridium nanoparticles with disk-shape (iridium nanodisks) were located between graphite layers; however, iridium nanoparticles on graphite surface were also formed in addition to iridium nanodisks in the Ir-GIC samples with 8 and 10 wt% iridium metal loadings. Iridium nanodisks between graphite layers were highly active for cinnamaldehyde hydrogenation and selective to cinnamyl alcohol compared with the iridium particles on graphite surfaces.

Graphical Abstract

Iridium nanoparticles with disk-shape structure were synthesized between graphite layers by thermal treatment of the mixture of iridium chloride and graphite under chlorine pressure followed by hydrogen reduction.

H-ZSM-5(RH) was synthesized using rice husk without an organic reagent and explored it as a support for Ni in the catalytic cracking of methane (CCM). Detailed investigations of the fresh and used catalysts analysed by using XRD, SEM, TEM, H₂-TPR, DT/TGA and CO pulse chemisorption techniques revealed that the high CCM activity was due to enhanced Ni dispersion and increased Cu-Ni interactions. Among the Ni/H-ZSM-5(RH) and bimetallic (Ni-M/H-ZSM-5(RH) M = Zn, Co, Fe, Cu) catalysts, the Cu-Ni/H-ZSM-5(RH) demonstrated a hydrogen yield of ~ 275 Nm³/mol_Ni which was explained by a high degree of graphitization confirmed by Raman spectroscopic analysis.

Light naphtha (C₅–C₆ alkanes) is commonly used as a feedstock for steam cracking or catalytic cracking to produce ethylene and propylene. This paper summarizes the progress of C₅/C₆ alkanes steam cracking and catalytic cracking, but the key problem of the above method is the high yield of low-value C₁–C₃ alkanes. When C₅/C₆ olefin is used as the feedstock of catalytic cracking, the ethylene and propylene yields are high, while the C₁–C₃ alkanes yield is low. It is of scientific value to dehydrogenate the C₅/C₆ alkanes into the corresponding olefins, and effectively convert the olefins into ethylene and propylene. This paper reviews recent progress of direct catalytic dehydrogenation and oxidative dehydrogenation of C₅/C₆ alkanes, and points out that the key is to develop C₅/C₆ alkanes dehydrogenation catalyst for selective preparation of corresponding mono-olefins. The main issues about how to develop highly selective C₅/C₆ alkanes dehydrogenation catalysts are proposed.

Nanostructured powders xFe/nano-Al₂O₃ with the Fe loading of x = 0.0 – 5.0 wt% were obtained using laser vaporization by CO₂ laser. XRF, XRD, HRTEM, PL and UV–Vis DRS techniques were employed to investigate physicochemical, structural and optical properties of the synthesized nanopowders with the average particle size of 9 nm. Nanopowders xFe/nano-Al₂O₃ as model catalysts were tested in isobutane dehydrogenation reaction. The results obtained were compared with similar data for the xFe/γ_Pb-Al₂O₃ systems synthesized by the conventional sol–gel method. According to XRD and UV–Vis DRS data, in the series of xFe/nano-Al₂O₃ samples a great part of Fe³⁺ ions is in the disordered environment of subsurface layers of Al₂O₃ nanocrystallites, predominantly in the tetrahedral coordination. In distinction to samples of the xFe/γ_Pb-Al₂O₃ series, in the case of nanostructured xFe/nano-Al₂O₃ powders the formation of Fe₂O₃ phase does not occur at any concentrations of iron or conditions of testing. The analysis of the PL spectra of xFe/nano-Al₂O₃ powders also showed the presence of surface sites of Fe³⁺ ions, which were not detected for xFe/γ_Pb-Al₂O₃. Catalytic testing of the xFe/nano-Al₂O₃ series samples in isobutane dehydrogenation revealed the formation of the iron active sites that ensure catalytic activity of the samples. Differences in the catalytic properties of FeO_x/Al₂O₃ samples obtained by the sol–gel method and laser vaporization are related to different states of Fe³⁺ ions. Thus, the xFe/nano-Al₂O₃ nanopowders, in contrast to xFe/γ_Pb-Al₂O₃, contain a large amount of active Fe³⁺ sites. These sites, being involved in the dehydrogenation reaction, are present predominantly on the surface of the nanopowders.

The production of aromatics with fuel properties from either biomass resources or low-cost refinery streams such as C5 is an important industrial interest. However, the strategic design of reliable catalysts with commercial compatibilities remained a challenge. Several investigations were carried out in this direction. This review accordingly presents a comprehensive analysis of the literature on the catalysis-based strategies adopted for aromatization of the feeds. Valorization of furans and allied oxygenates derived from biomass into aromatics was initially covered. The review examined strategies for C5 streams aromatization, co-upgrading of furans with hydrocarbons and methanol and discussed how biomass-derived bio-oils could be valorized into aromatics. In addition to discussion on the influence of catalytic textural, acidity and topological properties, the paper provided substantial updates on the associated reaction mechanisms. A perspective for further investigations in aromatization was also provided.

Traditional catalysts with one core and one shell structure have few active sites and shell structure parameters are difficult to be regulated. In order to solve these two problems, it is presented herein a multi-Pd-core and porous carbon shell catalyst mPd@HCS, where multiple Pd nuclei provide more active sites for the reaction, the shell structure parameters are tuned by the adjustment of shell thickness, and the influence of shell thickness on the performance of H₂O₂ direct synthesis was mainly investigated. The results showed that the selectivity and yield of H₂O₂ changed volcanically with the increase of carbon crust thickness because of the compromise between reactants diffusion and product degradation, and the selectivity (87%) and productivity (1938 mmol g_Pd⁻¹ h⁻¹) of the sample with middle shell thickness (10.18 nm) were the highest.

The catalytic properties and applications of Fenton and Fenton-like catalysts based on graphitic carbon nitride (g-C₃N₄) are reviewed. Compared with semiconductor photocatalytic, the synergistic system of photocatalysis and Fenton-like oxidation has a stronger ability to degrade organic wastewater, but there are still some shortcomings, such as high recombination rate of photogenerated carriers and serious agglomeration of metals on the catalyst surface, and its catalytic performance still needs to be further improved. The development of heterogeneous photo-Fenton-like catalysts based on g-C₃N₄ and their Fenton-like mechanism will be the focus of future research.

The over-consumption of petroleum fuel due to the progressive increase in population, transportation, industrialization, modernization as well as improvement in the lifestyle of the society leads to the fast declining of non-renewable resources. Therefore, it is important to discover low cost, environmentally friendly and sustainable surrogates of petroleum fuels. In this regard, biodiesel production is one of the gorgeous solutions for the research community. Contrary to the benefits, the high cost of the biodiesel is the main disadvantage, greatly reliant on the feedstock. In this sense, wild olive oil was explored for the first time as a suitable and novel feedstock for biodiesel technology development. The fatty acid composition was identified by GC–MS analysis whereas various physiochemical properties were determined by ASTM and EN methods. Furthermore, this review paper conveys a detailed overview of biodiesel production technologies, various generation feedstocks and types of catalyst along with their plausible mechanism.