Memory effect-enhanced catalytic ozonation of aqueous phenol and oxalic acid over supported Cu catalysts derived from hydrotalcite

Mg/Al supported metal (Fe, Co, Ni and Cu) oxide catalysts were prepared by co-precipitation of hydrotalcite-like clay materials as precursors, calcined, and used for the ozonation reaction of phenol and oxalic acid. The reaction was carried out using the catalyst and aqueous solution of phenol or oxalic acid in an O₃/O₂ mixed gas-flow at 20 °C. In the ozonation of phenol, the combination of ozone and supported metal oxide catalysts was effective for the removal of total organic carbon (TOC). Also in the ozonation of oxalic acid as the main TOC component, Cu/Mg/Al catalysts showed the highest activity, followed by Ni/Mg/Al catalyst, while both Fe/Mg/Al and Co/Mg/Al catalysts were not active. Leaching of Cu and Ni, probably due to the chelation of metals by oxalic acid, was significantly observed at the beginning of the reaction. However the metal leaching disappeared at the end of the reaction possibly due to the entire consumption of oxalic acid during the reaction. The best result of oxalic acid mineralization was observed over Cu/Mg/Al catalyst calcined at 600 °C, on which least leaching of the metal was detected. Moreover, a “memory effect” of hydrotalcite accelerated the mineralization of oxalic acid over the Cu/Mg/Al catalyst; oxalate anions were captured and decomposed in the reconstituted hydrotalcite interlayer space on the surface of the Cu/Mg/Al catalyst, resulting in a remarkable enhancement in the catalytic activity of the ozonation.     

Characterization and activity of novel copper-containing catalysts for selective catalytic reduction of NO with NH3

Cu/Mg/Al mixed oxides (CuO = 4.0–12.5 wt%), obtained by calcination of hydrotalcite-type (HT) anionic clays, were investigated in the selective catalytic reduction (SCR) of NO by NH₃, either in the absence or presence of oxygen, and their behaviours were compared with that of a CuO-supported catalyst (CuO = 10.0 wt%), prepared by incipient wetness impregnation of a Mg/Al mixed oxide also obtained by calcination of an HT precursor. XRD analysis, UV-visible-NIR diffuse reflectance spectra and temperature-programmed reduction analyses showed the formation, in the mixed oxide catalysts obtained from HT precursors, mainly of octahedrally coordinated Cu²⁺ ions, more strongly stabilized than Cu-containing species in the supported catalyst, although the latter showed a lower percentage of reduction. The presence of well dispersed Cu²⁺ ions improved the catalytic performances, although similar behaviours were observed for all catalysts in the absence of oxygen. On the contrary, when the mixture with excess oxygen was fed, very interesting catalytic performances were obtained for the catalyst richest in copper (CuO = 12.5 wt%). This catalyst exhibited a behaviour comparable to that of a commercial V₂O₅–WO₃TiO₂ catalyst, without any deactivation phenomena after four consecutive cycles and following 8 h of time-on-stream at 653 K. Decreasing the copper content or increasing the calcination time and temperature led to considerably poorer performances and catalytic behaviours similar to that of the CuO-supported catalyst, due to the side-reaction of NH₃ combustion on the free Mg/Al mixed oxide surface.     

Balancing acidity and basicity for highly selective and stable modified MgO catalysts in the alkylation of phenol with methanol

The alkylation of phenol was investigated over magnesium oxide catalysts modified with the addition of small amount of vanadium, manganese or other components. The catalytic performance was strongly dependent on the kinds of dopants due to changes in the acid–base properties. The modified MgO catalysts showed an activity higher than pure MgO catalyst. V–Mn–MgO catalyst was found to be more active and selective than that of V–Mgo or Mn–MgO catalyst for 2,6-xylenol. Among the modified catalysts, V–Mn–MgO catalyst was excellent in both phenol conversion and the selectivity to 2,6-xylenol. The alkylation of phenol in ortho position was explained in the acid–base property of mixed oxide. Phenol conversion and 2,6-xylenol selectivity increased with acidity, whereas the selectivity to o-cresol decreased because of the nature of the series reaction (phenol→o-cresol→2,6-xylenol→2,4,6-trimethylphenol (2,4,6-TMP)). Na–Mn–MgO catalyst prepared to achieve a balance between acidity and basicity was not deactivated and highly selective to o-cresol and 2,6-xylenol. Reaction temperature, feed composition and space velocity also significantly influenced the conversion and the selectivity in the alkylation of phenol.     

Catalytic Mononitration of Phenol Using <Emphasis Type="Italic">iso-</Emphasis>Propyl Nitrate Over Zeolite Catalysts

Mononitration of phenol was investigated using iso-propyl nitrate as a nitrating agent over various zeolite catalysts under different reaction conditions. Zeolite Hβ with a low Si/Al ratio (12.5) was found to be an active catalyst for nitration of phenol under reflux conditions in dichloroethane, producing 2- and 4-nitrophenols in a ratio of around 1:1. However, zeolites H-mordenite, HY and Hβ (with high Si/Al ratio—150 or 300) gave 2-nitrophenol as the major product (ortho/para ratio = ca. 2–3).     

FT-IR spectroscopic and catalytic study of de-aluminated H-mordenites as environmental friendly catalysts in the hydroxymethylation of 2-methoxyphenol with formaldehyde in aqueous medium

Several de-aluminated H-mordenites, prepared by treating a commercial H-mordenite (HM-16, Engelhard) with aqueous HCl solutions, were characterized and tested as catalysts in the liquid-phase hydroxymethylation of guaiacol with aqueous solutions of formalin, for the production of p-vanillic alcohol (3-methoxy-4-hydroxybenzyl alcohol), the intermediate in vanillin synthesis.

Samples were obtained with Si/Al atomic ratios from 10 to 36; their acidic and hydrophilic properties have been characterized by means of FT-IR spectroscopy of adsorbed probe molecules, namely CO at nominal 77 K, NH₃ and H₂O at room temperature, and ammonia TPD.

De-alumination led to the development of a mesoporous structure, and to a partial structure degradation with the most de-aluminated sample (Si/Al = 36).

As to the acidic properties, both Brønsted species in the main channels and in side-pockets were removed, and less acidic hydroxyls formed.

The catalytic performance was affected mainly by samples hydrophilicity that considerably decreased upon de-alumination. In the Si/Al ratio range investigated, a decrease in the number of acidic sites led to a complex catalytic behaviour, with a maximum activity for intermediate Si/Al ratio (=25). A higher concentration of aromatic compounds in the pores of more hydrophobic zeolites (higher Si/Al ratios) also led to a higher selectivity towards heavy, di-arylic by-products. A comparison with commercial H-mordenites having similar Si/Al ratio evidenced that the occurrence of mesoporosity, in strongly de-aluminated samples, also affected the catalytic performance, favouring the formation of bulky di-aryl compounds and leading to lower guaiacol conversion.     

Hydrogen peroxide modified Mg–Al–O oxides supported Pt–Sn catalysts for paraffin dehydrogenation

In this work, a new method to prepare Mg–Al–O oxide by co-precipitation method with addition of H₂O₂ was developed. The application of Mg–Al–O as a support of Pt–Sn catalysts for paraffin dehydrogenation was investigated. Characterization results indicated that modification of H₂O₂ (i) enlarged the pore structure and decreased the density and mechanical strength of the Mg–Al–O oxide and (ii) increased the platinum dispersion, weakened the acidity of the Pt–Sn/Mg–Al–O catalysts. Dehydrogenation of n-dodecane results showed that modification of H₂O₂ (iii) improved the paraffin conversion and olefin selectivity; (iv) inhibited the coke deposition on the catalyst and (v) extended the catalyst life-time.     

无模板法合成的Phi分子筛在NO选择性催化还原中的应用

氮氧化物（NO_x）是大气中的一种主要污染物。采用具有菱沸石结构（CHA）的铜基分子筛作为催化剂，通过选择性催化还原（SCR）技术可有效去除NO_x。采用一种经济环保的制备方法，在不使用模板剂的条件下水热合成一种具有结构缺陷的低硅铝比CHA型分子筛（Phi，Si/Al=4.7）。结果表明，经Cu离子交换制备的Cu/Phi具有最丰富的表面酸性与孤立态Cu²⁺，表现出较好的低温活性、较宽的工作温度窗口以及良好的水热稳定性。Na或Mg的存在降低了Cu/Phi的表面酸性及孤立态Cu²⁺的含量，水热老化后的Na，Cu/Phi和Mg，Cu/Phi均呈现出不同程度的骨架坍塌，相应导致了催化剂失活。     

Chemicals from biomass: Synthesis of glycerol carbonate by transesterification and carbonylation with urea with hydrotalcite catalysts. The role of acid–base pairs

Synthesis of glycerol carbonate has been performed by transesterification of ethylene carbonate with glycerol catalyzed by basic oxides (MgO, and CaO), and mixed oxides (Al/Mg, Al/Li) derived from hydrotalcites. The results showed that the optimum catalyst in terms of activity and selectivity is a strong basic Al/Ca-mixed oxide (AlCaMO) which is able to catalyze the reaction at low temperature (35 °C), and low catalyst loading (0.5 wt%) giving high glycerol conversions with 98% selectivity to glycerol carbonate. When the synthesis of glycerol carbonate was carried out by carbonylation of glycerol with urea, the results showed that balanced bifunctional acid–base catalysts where the Lewis acid activates the carbonyl of the urea and the conjugated basic site activates the hydroxyl group of the glycerol were the most active and selective catalysts.     

Phi zeolite synthesized by template-free method for selective catalytic reduction of NO

Nitrogen oxide (NO_x) is one of the major air pollutants. Using a copper-based zeolite with a chabazite structure (CHA) as a catalyst, the selective catalytic reduction (SCR) technology can effectively remove NO_x. This work introduces a low silica CHA type zeolite with structural defects (zeolite Phi, with Si/Al of 4.7). The zeolite Phi is synthesized through a hydrothermal method without adding any template, which is low-cost and environment-friendly. The Cu-exchanged Phi is abundant of surface acidity and isolated Cu²⁺, showing a superior low-temperature activity, a wide work temperature window and a good hydrothermal stability. The presence of Na or Mg decreases the surface acidity and isolated Cu²⁺. The hydrothermally aged Na,Cu/Phi and Mg,Cu/Phi present different levels of framework collapse, which correspondingly induces catalyst deactivation.     

Partial Oxidation of Methane to Syngas over Calcined Ni–Mg/Al Layered Double Hydroxides

The catalytic partial oxidation of CH₄ to syngas was carried out over an Ni–Mg/Al mixed-oxide catalyst prepared from layered double hydroxide-type precursors. The catalysts were characterized by XRD, TPR, UV-DRS, XRF, BET and CHNS analysis. The effects of the catalyst composition and the calcination temperature on the catalytic performance and the extent of catalyst deactivation were investigated. Ni–Mg/Al oxide catalysts converted CH₄ into syngas efficiently with high selectivity. The catalyst performance was strongly related to the Ni particle size and the calcination temperature. The catalysts that were calcined at higher temperature exhibited a better catalytic performance. In conclusion, the NiAl₂O₄ spinel phase had a positive effect on the stability of the catalyst.     

Novel low temperature NOx storage-reduction catalysts for diesel light-duty engine emissions based on hydrotalcite compounds

A series of Pt and Pt,Cu supported catalysts were prepared by wet impregnation of Mg–Al supports obtained from hydrotalcite-type (HT) precursor compounds. These novel NO_x storage-reduction (NO_xSR) catalysts show improved performances in NO_x storage than Pt,Ba/alumina NO_xSR catalysts at reaction temperatures lower than 200 °C. These catalysts show also improved resistance to deactivation by SO₂. The effect is attributed to the formation of well dispersed Mg(Al)O particles which show good NO_x storage properties. The promoted low temperature activity is explained by the lower basicity of the Mg(Al)O mixed oxide in comparison to BaO, which induces on one hand a lower inhibition on Pt activity (NO to NO₂ oxidation and/or hydrocarbon oxidation) due to electronic effect, and on the other hand a lower thermal stability of the stored NO_x. The presence of Cu slightly inhibits activity at low temperature, although improves activity and resistance to deactivation at 300 °C. On these catalysts FT-IR characterization evidences the formation of a Pt–Cu alloy after reduction.     

Chemistry, spectroscopy and the role of supported vanadium oxides in heterogeneous catalysis

Supported vanadium oxide catalysts are active in a wide range of applications. In this review, an overview is given of the current knowledge available about vanadium oxide-based catalysts. The review starts with the importance of vanadium in heterogeneous catalysis, a discussion of the molecular structure of vanadium in water and in the solid state and an overview of the spectroscopic techniques enabling to study the chemistry of supported vanadium oxides. In the second part, it will be shown that advanced spectroscopic tools can be used to obtain detailed information about the coordination environment and oxidation state of vanadium oxides during each stage of the life-span of a heterogeneous catalyst. Three topics will be discussed: (1) the molecular structure of supported vanadium oxide catalysts under hydrated, dehydrated and reduced conditions, including the parameters, which influence the molecular structures formed at the surface of the support oxide; (2) elucidation of the active surface vanadium oxide during the oxidation of methanol to formaldehyde, the reaction mechanism and the vanadium oxide---support effect; and (3) deactivation of fluid catalytic cracking (FCC) catalysts by migration of vanadium oxides and the development of a method preventing the structural breakdown of zeolites by trapping the mobile vanadium oxides in an aluminum oxide coating.     

含铁复合金属氧化物对苯酚羟基化反应工艺的研究

在连续全混反应器中 ,用含铁复合金属氧化物催化剂 ,研究了反应温度、空速、过氧化氢 /苯酚对反应产物中苯二酚浓度、邻苯二酚 /对苯二酚比例和催化剂的活性周期的影响。试验结果表明 ,反应温度对反应产物中邻苯二酚 /对苯二酚的比例和催化剂的活性周期的影响不明显 ,过氧化氢 /苯酚摩尔比对邻苯二酚 /对苯二酚的比例的影响较大 ,提高过氧化氢 /苯酚摩尔比会降低邻苯二酚 /对苯二酚的比例 ,缩短催化剂的活性周期     

Short Vapour Residence Time Catalytic Pyrolysis of Spruce Sawdust in a Bubbling Fluidized-Bed Reactor with HZSM-5 Catalysts

Catalytic pyrolysis of spruce sawdust was carried out in a bubbling fluidized-bed reactor using HZSM-5 catalysts. The effects of space velocity, catalyst deactivation, catalyst acidity and catalyst regeneration were studied. The use of catalysts decreased the yield of organic liquids compared to non-catalytic yields while the yields of pyrolytic water and gases increased. Decreasing the space velocity enhanced these effects. The rate of catalyst deactivation depended on the acidity of the catalyst, with more acidic catalysts deactivating more rapidly. Using a catalyst with a Si/Al ratio of 140 resulted in the largest changes in bio-oil properties. Periodic regeneration of the catalyst in the fluidized-bed reactor was also demonstrated using varying regeneration times and temperatures. It was shown that compared to BFB reactors, CFB reactor types would offer better operating characteristics for commercial scale catalytic pyrolysis processes in regard to vapour residence times, and catalyst activity and regeneration.     

Gas-phase conversion of glycerol over mixed metal oxide catalysts

A series of aluminophosphates (APO) catalysts with Ce, Cu, Cr, Fe, Mn, Mo, V, and W oxide loading at a constant ratio M: Al = 1: 10 and PO₄: Al = 1: 12 were prepared and characterized by N₂ physisorption, XRD and NH₃-TPD. Gas-phase dehydration of glycerol to produce acrolein and acetol was investigated at 280°C in presence of water. Conversion and product distribution depended on the intrinsic acidity and the type of transition metal oxide. Best selectivity to acrolein (52–58%) was obtained for W- und Mo-APO catalysts. Cr-, Mn- and W- oxide containing catalysts enhanced the formation of phenol, acetaldehyde and CO _x . The catalysts containing V- and Fe-oxide promoted the formation of allyl alcohol. All catalysts showed long term stability, which can be attributed to the redox ability of the metal oxides that enhances the removal of coke deposits. The investigated catalyst a specially W-APO and Mo-APO can be recommended for further controlled trials on a pilot plant for selective conversion of water solution of glycerol to acrolein and/or acetol.     

在丙烯氨氧化反应中Sb-Fe氧化物催化剂的结炭及失活

在装有10ml催化剂的沸腾床反应器中研究了丙烯氨氧化Sb-Fe催化剂的结炭过程和结炭的影响,通过对Sb-Fe催化剂和国外工业化的催化剂的反应性能、表面酸度、表面积、平均孔径、ESR和丙烯与氧的化学吸附及丙烯的TPD等物理化学测定以及丙烯腈-2-~（14）C的同位素实验,证明了反应物及中间物在选择氧化的活性中心上的结炭是催化剂失活的主要原因,并且Sb-Fe氧化物催化剂具有易还原和不易再氧化的性质,在低氧气氛中易于引起活性结构的破坏。根据以上的结论提出了改进催化剂的方向。     

Study of the accessibility effect on the irreversible deactivation of FCC catalysts from contaminant feed metals

Two commercial FCC catalysts were investigated to explore the effect of their different accessibility on the catalyst activity, selectivity and deactivation due to deleterious feed metals (V and Ni). Feed metal Fe was not included in the present study. E-Cats (equilibrium samples from a commercial FCC unit) of both FCC catalysts and the corresponding laboratory-deactivated samples (applying the cyclic deactivation (CD) and the cyclic propylene steaming (CPS) methods) were thoroughly studied. Extensive characterization (XRD, N₂ physisorption, measurement of Akzo Accessibility Index (AAI), SEM-EDS analysis) of all samples was realized to investigate variations in their crucial properties due to metal deposition. Comparison of E-Cats, CD and CPS samples revealed a very different nickel deposition profile over the CPS samples. In all cases, V was homogenously distributed throughout the particle, as expected due to its mobility. Ni–Al mixed phases, observed on the E-Cat samples, were probably formed during ageing and are expected to be inactive. The absence of such phases on the laboratory-deactivated samples can be attributed both to the inability of the two deactivation methods to simulate metal ageing during commercial utilization of the FCC catalyst and the absence of Fe incorporation during laboratory deactivation. All catalytic samples (E-Cats and artificially deactivated FCC catalysts) were evaluated in the laboratory using two bench-scale Microactivity Test (MAT) units of different reactor configuration: fixed-bed (SCT-MAT unit) and fluid-bed (AUTOMAT unit). Similar ranking of the catalysts is achieved when using both units. However, AUTOMAT unit seems to provide a clearer diversification of catalysts with different accessibility. Both laboratory deactivation methods seem to be rather inefficient in simulating the real deactivation, since they are always exaggerating metal effects.     

基于镁铝水滑石的Mo/Al2O3-MgO催化剂制备及其加氢脱硫性能

生产低硫或无硫柴油是当今世界范围内清洁燃料发展的趋势,加氢脱硫（HDS）是大规模生产清洁柴油最为有效的技术之一,而研制高活性的HDS催化剂成为该技术的关键。以镁铝水滑石与氧化铝的复合氧化物为载体,通过等体积浸渍法制备了一系列Mo/Al₂O₃-MgO催化剂,以二苯并噻吩（DBT）的正庚烷溶液为原料,在固定床反应器上评价所得催化剂的HDS活性,考察了不同镁铝比的水滑石、焙烧温度和添加量对催化剂物化性质和催化性能的影响。研究结果表明,镁铝比、焙烧温度和添加量均影响催化剂的酸性、金属还原性、硫化性能和MoS₂片晶的堆垛度等,当镁铝摩尔比为3、焙烧温度为800℃、成型时水滑石加入量为10%（质量分数）时,所制备催化剂的HDS活性最高,其脱硫率可达96.2%。这是由于该催化剂的酸性较适宜,活性组分与载体间的相互作用力适中,活性组分更易硫化,有助于提高MoS₂片晶的堆垛度进而改善催化剂的HDS性能。     

Catalytic effects during cellulose liquefaction

Cellulose can be totally liquefied by heating to 350 °C in the presence of an aqueous phenolic solvent containing a catalyst. The main products are light aromatic hydrocarbons, benzofurans, heavier aromatic hydrocarbons such as substituted indanes and tetralin, and xanthenes. The variation of product distribution with catalyst was examined and it was found that in aqueous phenol, xanthene formation was enhanced by acidity. By substituting guaiacol for phenol, it was determined that most benzofuran formation involved the phenol solvent molecules, although a small proportion did not. This benzofuran may have arises from phenol generated from cellulose, the incorporation of phenol in the products being enhanced through a cage effect.     

Dehydrogenation of ethylbenzene with carbon dioxide over MgO-modified Al2O3-supported V–Sb oxide catalysts

Alumina-supported V_0.43Sb_0.57 oxide (VSb/Al) and MgO-modified alumina-supported V_0.43Sb_0.57 oxide catalysts (VSb/Mg_nAl with Mg/Al atomic ratio, n = 0.1, 0.3 or 0.5) have been tested for the dehydrogenation of ethylbenzene with carbon dioxide as an oxidant. Their catalytic behaviors were interpreted by results of several catalyst characterization methods. The decrease in the surface acidity of the VSb/Mg_nAl catalysts due to modification of alumina with MgO favors the prolonged time-on-stream activities. However, the addition of relatively large amounts of MgO (n = 0.3 or 0.5) causes substantial decrease in their surface areas, reducibility of active vanadium oxide component and, consequently, ethylbenzene conversion. These negative factors did not become apparent for the most efficient VSb/Mg_0.1Al system demonstrating high and stable catalytic activity.