Regulating metal–acid active sites in hierarchical porous Ni/Y for selective hydrocracking of naphthalene

Phosphate and nitrate were loaded on silica BEA (P/HSi@BEA and N/HSi@BEA), which is fibrously protonated by the impregnation method for n-hexane and cyclohexane isomerization. The characterization analysis specified the removal of tetrahedral aluminum atoms in the framework, which was triggered by the existence of phosphate and nitrate groups in the catalyst. The exchanged role of Si(OH)Al to P-OH as active acidic sites in the P/HSi@BEA catalyst reduced its acidic strength, which was confirmed by the FTIR results. Lewis acidic sites of P/HSi@BEA performance are a significant part in the generation of high protonic acid sites, as proven by the in situ ESR study. However, FTIR evacuation and 27Al NMR revealed that the reduction in the amount of extraframework Al (EFAl) is due to its interaction with the nitrate group on the outside of the catalyst surface. The N/HSi@BEA catalyst exhibited high acidic strength because of the existence of more Si(OH)Al, which was initiated during the nitrate-incorporation process. Of significance is that the catalytic performance of n-hexane isomerization in the presence of hydrogen reached 50.3% product isomer yield at 250 °C, which might be ascribed to the presence of P-OH active sites that are responsible for accepting electrons, forming active protonic acid sites. NO3-EFAl interaction induced the formation of Brønsted acid sites, and higher mesopore volume favors the production of cyclohexane isomers up to 48.4% at 250 °C. This fundamental study exhibits that significant interactions given by such phosphate and nitrate groups with the unique silica fibrous BEA support could enhance isomerization, which contributes to the high quality of fuel.

Modern heterogeneous catalysts for biodiesel production: A comprehensive review

A review of biomass-derived heterogeneous catalyst for a sustainable biodiesel production

The combination poisoning effect of KCl and ZnCl2 on V2O5-WO3/TiO2deNOx catalyst

For a long time, many chemical reactions drew on catalysts, products used in smallest quantities compared to products-reagents, to accelerate their kinetics. In certain cases, one of the determining factors to improve these catalysts activities is the use of supports allowing dispersions and thereafter the effectiveness of its active sites.. It is the goal of our study, to increase the pine wood powders value like support of active acid H+ sites of sulphuric acid molecules by hydrogen bond connection with alkenes of aromatics and polynuclear aromatics which were pine wood components and their derivatives obtained after sulphuric acid solution (98%) treatment. Among these derivatives we quote water molecules formed during dehydration and esterification of wood components. Thus, we obtained homogeneous catalysts BXH+, (H+/H2SO4) supported on pine wood powder which we tested by a test reaction: citric acid dehydration to prop-1-ene 1, 2, 3 acid- tricarboxylic acid. Also, the active acid sites (H+/H2SO4) contents and alkenes on BXH+ catalysts were quantified by measuring out respectively with NaOH 0.05N and hydrofluoric acid (HF). This last measuring out enabled us to evaluate the nature of the aromatics and polynuclear aromatics which were the real supports contained in pine wood. At the end, we used these BXH+ synthesized catalysts to catalyze the citric acid black polymer synthesis (PN). The soluble coke and insoluble coke in polar solvent dichloromethane and non-polar solvent hexane of citric acid black polymer synthesized by each catalyst were quantified.

Limited by harsh reaction conditions, the activation and utilization of methane were regarded as holy grail reaction. Co-reaction with methanol, successfully realizing mild conversion below 450 °C, provides practical strategies for methane conversion on metal-loaded ZSM-5 zeolites, especially for highly efficient Zn loaded ones. However, Zn species, regarded as active acid sites on the zeolite, have not been sufficiently studied. In this paper, Zn-loaded ZSM-5 zeolite was prepared, and Zn was modified by capacity, loading strategy, and treating atmosphere. Apparent methane conversion achieves 15.3% for 1.0Zn/Z-H2 (16.8% as calculated net conversion) with a significantly reduced loading of 1.0 wt.% against deactivation, which is among the best within related zeolite materials. Besides, compared to the MTA reaction, the addition of methane promotes the high-valued aromatic production from 49.4% to 54.8%, and inhibits the C10+ production from 7.8% to 3.6%. Notably, Zn2+ is found to be another active site different from the reported ZnOH+. Medium strong acid sites are proved to be beneficial for methane activation. This work provides suggestions for the modification of the Zn active site, in order to prepare highly efficient catalysts for methane activation and BTX production in co-reaction with methanol.

Development of transition metal oxide-zeolite catalysts to control chlorinated VOC air emissions

Supported CoW bifunctional catalyst with high activity and selectivity for hydrocracking alkane

Scaling of lignin monomer hydrogenation, hydrodeoxygenation and hydrocracking reaction micro-kinetics over solid metal/acid catalysts to aromatic oligomers

Enhanced gasoline selectivity through Fischer-Tropsch synthesis on a bifunctional catalyst: Effects of active sites proximity and reaction temperature

Structure-performance relationship of NiMo/Al2O3-HY catalysts in selective hydrocracking of poly-aromatics to mono-aromatics

The conversion of light alkanes to high value aromatics proceeds with a high selectivity over bifunctional, gallium (Ga) containing zeolite catalysts. It is generally agreed that Ga sites are involved in dehydrogenation reaction steps and that the zeolite acid sites catalyze cracking, oligomerization, and cyclization reactions. However, understanding of the precise roles of the acid and Ga sites in the reaction mechanisms is significantly hampered since the number of these sites in working catalysts is not known. This paper describes a kinetic approach to evaluation of the acid and Ga active sites in working Ga containing TON zeolite catalysts that relies on the analysis of the rates of formation of the primary products of a n-butane aromatization reaction. Our results show that the rate of ethane formation at low n-butane conversions can be used as a quantitative estimate of acidity in working bifunctional zeolite catalysts and demonstrate, for the first time, a significant decrease in the number of Brønsted acid sites in the Ga containing catalysts under reaction conditions: around 47 and 79% for the catalysts with Ga loading of 1.5 and 2.5 wt %, respectively. We conclude that the reduction in acidity is associated with the formation of catalytically active Ga(+) ions and obtain estimates for the number and steady-state turnover activity of the acid and Ga active sites in n-butane transformation. We anticipate that our work will facilitate understanding of the precise roles of the acid and Ga sites in the mechanisms of alkane aromatization and, as a far-reaching implication, will prompt wider use of detailed kinetic studies for the evaluation of active sites in working catalysts.

The acid–base properties of vanadium phosphate catalysts are investigated using the aldol condensation of acetone and the reactions of 2-methylbut-3-yn-2-ol (MBOH) over alkali-doped vanadium phosphate catalysts. Two well defined vanadium phosphates were investigated, namely (VO)2P2O7 and δ-VOPO4. Alkali-doped (VO)2P2O7 was prepared by heating alkali-doped VOHPO4·0.5H2O in He (8 h, 750 °C), and Na+-, K+- and Cs+-doped samples were investigated. The reaction of MBOH was used to probe the acid–base nature of the surface sites. The undoped V4+ (VO)2P2O7 exhibited only acidic active sites, whereas when doped with 10% Na+, K+ or Cs+ the active sites became predominantly basic in nature. Both the doped and undoped samples were selective for the formation of isophorone (selectivity 90%) from the aldol condensation of acetone, and the Cs-doped and undoped (VO)2P2O7 exhibited similar intrinsic activities (mol(isophorone) m−2 h−1). In contrast, alkali-doping of the V5+ vanadium phosphate γ-VOPO4 did not induce the formation of a significant number of surface basic sites and the active sites for MBOH decomposition remained predominantly acidic in nature. Both the doped and undoped δ-VOPO4 were non-selective in the aldol condensation of acetone, and during the short-lived reaction, only hydrocarbons (typically isobutane and isobutene) were observed. The results are discussed with respect to the nature of active sites for the selective oxidation of n-butane to maleic anhydride.

The Lewis acid properties of a series of isolated and well-defined Sn centers in different micro- and mesoporous materials have been investigated by means of DFT calculations and IR spectroscopy of probe molecules, and the results have been related to the experimentally measured catalytic activity of these materials for different reactions. Different types of Sn centers have been detected and modelled: inactive fully coordinated Sn atoms in framework positions that weakly interact with Lewis bases, and highly active strong Lewis acid sites associated with Sn centers with one or two hydrolyzed Sn-O-Si bridges. The relative amount of strong and weak sites depends on the zeolite structure, and can be modified by the catalyst pre-treatment conditions. On the other hand, it has been established that Sn-containing mesoporous materials obtained either by direct synthesis or by post-synthesis incorporation of Sn, show a similar distribution of centers. Finally, the influence of solvent and free space available around the active site on the diastereoselectivity of the cyclization of citronellal to isopulegol were investigated, and some hints were obtained on how to improve the catalyst performance.

WO3 monolayer loaded on ZrO2: Property–activity relationship in n-butane isomerization evidenced by hydrogen adsorption and IR studies