Effect of Additives on the Physicochemical and Catalytic Properties of Oxide Catalysts in Selective Oxidation Reactions

This paper is a survey of the main facts and concepts concerning the effect of additives on the structure and physicochemical and catalytic properties of oxide catalysts in selective oxidation reactions. The phenomena occurring in monophasic and supported mixed oxides containing the additives, including modification of structure, solid state reactions, segregation, defect formation, and spill-over of the reactants, are briefly described. The effect of additives on acid--base and redox properties, and on their bearing on catalytic performance are discussed, with particular emphasis on alkali metal additives. The perspectives of further studies on the problem are proposed.     

Selective Oxidation of Methanol to Formaldehyde Using Modified Iron-Molybdate Catalysts

Methanol selective oxidation to formaldehyde over a modified Fe-Mo catalyst with two different stoichiometric (Mo/Fe atomic ratio = 1.5 and 3.0) was studied experimentally in a fixed bed reactor over a wide range of reaction conditions. The physicochemical characterization of the prepared catalysts provides evidence that Fe₂(MoO₄)₃ is in fact the active phase of the catalyst. The experimental results of conversion of methanol and selectivity towards formaldehyde for various residence times were studied. The results showed that as the residence time increases the yield of formaldehyde decreases. Selectivity of formaldehyde decreases with increase in residence time. This result is attributable to subsequent oxidation of formaldehyde to carbon monoxide due to longer residence time.     

Efficient Copper-bisisoquinoline-based Catalysts for Selective Aerobic Oxidation of Alcohols to Aldehydes and Ketones

The selective oxidation of alcohols with molecular oxygen was efficiently completed in high conversion and selectivity using copper-bisisoquinoline-based catalysts under mild reaction condition. The effects of various parameters such as reaction temperature, reaction time, oxidant, ligands, etc, were studied. Solvent effect has been as well studied in ionic liquids [bmim]PF₆, [omim]BF₄ and [hmim]BF₄, comparing to traditional volatile organic solvent. The use of ionic liquids was found to enhance the catalytic properties of the catalysts used.     

Selective Production of Hydrogen for Fuel Cells Via Oxidative Steam Reforming of Methanol Over CuZnAl Oxide Catalysts: Effect of Substitution of Zirconium and Cerium on the Catalytic Performance

H₂ fuel, for fuel cells, is traditionally produced from methanol by the endothermic steam reforming of methanol (SRM). Partial oxidation of methanol (POM), which is highly exothermic, has also been suggested as a route to extract H₂ from methanol. In both these reactions a considerable amount of CO is produced as a byproduct, which is a poison to the Pt anode of the fuel cell. A combined steam reforming and partial oxidation of methanol, which has been termed oxidative steam reforming of methanol (OSRM), reported recently is considered to be more efficient and convenient for the selective production of H₂ at a relatively low temperature. The catalysts used in the OSRM reaction were CuZnAl mixed oxides derived from hydroxycarbonate precursors containing hydrotalcite (HT)-like layered double hydroxides (LDHs)/aurichalcite phases. Substitution of Zr for Al in the CuZnAl oxide system was found to improve the catalytic performance. In the present study, the role of added Zr was investigated in detail by employing spectroscopic methods such as X-ray diffraction (XRD), temperature-programmed reduction (TPR), electron paramagnetic resonance (EPR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and X-ray induced Auger electron spectroscopy (AES). The detailed spectroscopic studies revealed that substitution of Zr for Al improved the reducibility and dispersion of copper species due to the operation of a synergistic interaction between copper and zirconium as a consequence of the formation of a Cu²⁺-O-Zr⁴⁺-O- solid solution. The higher catalytic performance of CuZn-based catalysts containing Zr in the OSRM reaction was attributed to the ease of reducibility and enhanced dispersion of copper particles on the support. The substitution of Ce in the CuZnAl system, on the other hand, did not alter the catalytic performance greatly.     

Influence of Zirconia Promoter on Catalytic Properties of Cu–Cr–Si Catalysts for Methanol Synthesis at High CO Conversion in Slurry Phase

The low-temperature methanol synthesis was studied using novel Cu–Cr–Si catalysts promoted by zirconia at 115 °C and 3.0 MPa in slurry phase. Zirconia addition improved significantly the catalytic performance. From the characteristic results, copper and chromium were enriched on the catalyst surface and more Cu⁺ cations were stabilized by the zirconia promotion.     

Transfer and Reaction Performances of Selective Catalytic Reduction of N2O with CO over Monolith Catalysts

This work tries to identify the relationship between geometric configuration of monolith catalysts, and transfer and reaction performances for selective catalytic reduction of N2O with CO. Monolith cat...     

用于控制CO2氨法捕获过程中NH3逸出的选择性催化氧化（SCO）催化剂

利用NH3选择性催化氧化(NH3-SCO)方法控制电站CO2氨法捕获过程中的NH3逸出具有良好的应用前景,但用于该方法的催化剂应该具有高低温活性、高N2选择性高、长耐久性和低成本等特性。为推进NH3-SCO技术的实用化进程,本文在文献研究的基础上,总结了几种NH3-SCO催化剂的组成、不同催化剂和不同运行条件下NH3-SCO的特性和机理以及能提升催化效果的助剂,以期为探索合适的新型催化剂和新型反应器结构提供参考。文献研究表明,Ag/Al2O3是一种具有良好低温活性的NH3-SCO催化剂,但需具备Fe-ZSM-5所具有的高N2选择性,同时,还可以考虑利用一些物质如Ce可以用来进一步提升Ag/Al2O3的低温活性。     

Flame-made Alumina Supported Pd–Pt Nanoparticles: Structural Properties and Catalytic Behavior in Methane Combustion

Bimetallic palladium–platinum nanoparticles supported on alumina were prepared by flame spray pyrolysis. The as-prepared materials were characterized by scanning transmission electron microscopy (STEM), CO chemisorption, nitrogen adsorption (BET), X-ray diffraction (XRD), temperature programmed reduction (TPR), thermogravimetric analysis (TGA) and extended X-ray absorption fine structure (EXAFS) spectroscopy. The materials were tested for the catalytic combustion of methane with a focus on the thermal stability of the noble metal particles. After flame synthesis the noble metal components of the materials were predominantly in oxidized state and finely dispersed on the alumina matrix. Reduction afforded small bimetallic Pd–Pt alloy particles (< 5 nm) supported on Al₂O₃ ceramic nanoparticles. The addition of small amounts of platinum made the palladium particles more resistant against sintering at high temperatures and further lowered the deactivation observed during methane combustion.     

Propane Oxidation on MoVTeNbO Mixed Oxide Catalysts: Study of the Phase Composition of Active and Selective Catalysts

Several phases reported as minor or major phases in the active MoVTeNbO catalysts have been prepared and investigated for the oxidation of propane into acrylic acid. Activity and selectivity of pure phases and mixtures of phases obtained either directly from synthesis or by co-grinding have been compared. The results obtained confirmed that the orthorhombic M1 phase is the most active and selective phase and is responsible for the major part of the efficiency of the best catalysts. However, they also clearly demonstrated that a synergism due to a cooperation between phases occurs, similar to that previously proposed between the M1 [(Te₂O)M₂₀O₅₆] and M2 [(TeO)M₃O₉] phases for the ammoxidation of propane. The origin of this phase cooperation is discussed.     

Combining XRD and EXAFS with on-Line Catalytic Studies for in situ Characterization of Catalysts

Advances in the study of catalysts by in situ structural characterization, using X-ray absorption spectroscopy (XAFS) and X-ray diffraction (XRD), have recently been achieved and they are illustrated by reference to several examples. Emphasis in the present overview is laid on the study of catalysts under realistic working conditions and therefore in particular on-line gas analysis during activation and/or during catalysis. The examples encompass (a) activation of copper-based methanol catalysts, (b) dynamic changes of copper-based catalysts during methanol synthesis conditions, (c) catalytic partial oxidation on Rh/Al₂O₃ catalysts, and (d) reduction (activation) of copper-promoted high temperature shift catalysts.     

Effect of Pd on Cu-Zn Catalysts for the Hydrogenation of CO2 to Methanol: Stabilization of Cu Metal Against CO2 Oxidation

A palladium–copper–zinc catalyst (PdO:CuO:ZnO=2:28:70), prepared by sequential precipitation of the respective cations, was tested in the hydrogenation of CO₂ at high pressure (conditions: 60 bar, CO₂:H₂=1:3 (molar), W/F=0.0675 kg h/m³, 453-513 K). The methanol yield was improved on using this Pd-containing catalyst at all temperatures with respect to the reference copper–zinc catalyst (CuO:ZnO=30:70). This improvement was not due to an additional effect in which palladium was acting as an independent catalytic site but was caused by a synergetic effect of Pd on the active Cu sites. This effect was explained in terms of hydrogen spillover and an increased stability against CO₂ oxidation of the surface copper. Therefore, the present contribution not only supports previous literature findings concerning the hydrogen spillover mechanism but also resulted in a complementary view regarding the role of palladium in Pd-modified CuO-ZnO-based catalysts.     

催化法烟气同时脱硫脱氮技术研究进展

通过综述近年来研究较多的以催化法为基础的同时脱硫脱氮技术,包括基于SCR同时脱硫脱氮工艺和液相催化氧化技术,并介绍了各种工艺的特点,提出了催化法同时脱硫脱氮技术中存在的问题和今后的研究方向。     

Quasicatalytic and catalytic selective oxidation of methane to methanol over solid materials: a review on the roles of water

ABSTRACT

To date, although no commercial process for the selective oxidation of methane has been realized, various novel processes with effective solid materials operated at low temperature have been proposed. It is found that the addition of water in any processes not only influences the activity, selectivity, and stability of the solid materials but also affects the extraction efficiency of methanol from the product. Herein, the published results on the roles of water in the methanol production via the quasicatalytic and catalytic selective methane oxidation process using various solid materials in gas and liquid phases at low temperatures are critically reviewed.     

Catalytic Performance of the Sb–V Mixed Oxide on Sb–V–O/SiO2 Catalysts in Methane Selective Oxidation to Formaldehyde

Sb–V–O/SiO₂ catalysts were prepared and investigated in methane selective oxidation with O₂ as oxidant. Sb–V–O/SiO₂ catalysts are active and selective in methane selective oxidation. The formaldehyde yield obtained on Sb–V–O/SiO₂ catalysts is clearly higher than that for VO_X/SiO₂ and SbO_X/SiO₂ catalysts. A one-pass formaldehyde yield up to 3% was obtained on Sb–V–O/SiO₂ catalysts at 650 °C. XRD and UV Raman studies showed that the phase of Sb–V mixed oxide on Sb–V–O/SiO₂ catalysts transformed with decreasing Sb/V ratio from Sb₂VO₅ to SbVO₄/VSb_1-XO_4-1.5X phase. The Sb–V mixed oxide in Sb₂VO₅ phase is more active and selective than that in SbVO₄/VSb_1-XO_4-1.5X phase.     

Low-Temperature Methanol Synthesis in Catalytic Systems Composed of Copper-Based Oxides and Alkali Alkoxides in Liquid Media: Effects of Reaction Variables on Catalytic Performance

Catalytic systems composed of copper-based oxides and alkali alkoxides are tested for low-temperature methanol synthesis in liquid phases, which involves carbonylation of methanol to methyl formate and consecutive hydrogenation of methyl formate to methanol. The effects of reaction variables on the catalytic performance are investigated under the conditions of 373-423K temperature and 1.5-5.0 Mpa pressure. The combined catalytic systems of copper chromite and potassium methoxide exhibit excellent activities for the production of methanol. Higher values of reaction temperature, initial pressure, catalyst loading, and H₂/CO ratio of the feed gas lead to higher methanol productivity. In particular, the reaction temperatures and the feed gas compositions strongly influence the catalytic performance. No methanol is formed when employing a feed gas containing 2% CO₂. The catalytic systems are deactivated in a short period even in a CO₂-free feed gas, due to the consumption of the alkoxide component. Alkali alkoxides are consumed through reactions with trace amounts of CO₂ and H₂O which are formed as by-products during the course of the runs. The results also suggest that the hydrogenation step of methyl formate over copper chromite is greatly accelerated in the presence of the alkali alkoxide.     

油头日产1000吨氨装置改天然气1200吨氨和330吨甲醇的设计方案

从汕头改成气头制氨,有两种改造方案,一是天然气非催化转化法,二是天然气催化转化的蒸汽转化串纯氧部分氧化法。欲充分利用设备能力,年生产３６万吨氨和联产１０万吨甲醇,做到节能、节气、降低投资、提高效益、即可达到增加产品和产量目的     

Noble Metal (Pt, Rh, Pd) Promoted Fe-ZSM-5 for Selective Catalytic Oxidation of Ammonia to N2 at Low Temperatures

We have reported previously the excellent performance of Fe-exchanged ZSM-5 for selective catalytic oxidation (SCO) of ammonia to nitrogen at high temperatures (e.g., 400-500 °C). The present work indicates that the reaction temperature can be decreased to 250-350 °C when a small amount of noble metal (Pt, Rh or Pd) is added (by both doping and ion exchange) to the Fe-ZSM-5. The SCO activity follows the order: Pt/Fe-ZSM-5 > Rh/Fe-ZSM-5 > Pd/Fe-ZSM-5. The noble metal promoted Fe-ZSM-5 catalysts also show higher activity for NH₃ oxidation than Ce-exchanged Fe-ZSM-5 at low temperatures. On the Pt promoted Fe-ZSM-5, near 100% of NH₃ conversion is obtained at 250 °C at a high space velocity (GHSV = 2.3 × 10⁵ h^-1) and nitrogen is the main product. The presence of H₂O and SO₂ decreases the SCO performance only slightly. This catalyst is a good candidate for solving the ammonia slip problem that plagues the selective catalytic reduction (SCR) of NO with ammonia in power plants.     

Selective Deep Catalytic Cracking Process of Hydrocarbon Feedstocks for the Production of Light Olefins: II. Cooperative Effect of Thermal Cracking and Catalytic Reactions Observed in a 1-Zone Reactor

Hybrid catalysts comprising a chromium-based cocatalyst and a silica-rich ZSM-5 zeolite, when doped with lithium, showed quite a high on-stream stability even at a relatively high reaction temperature (735 °C). The cooperative effect of the thermal cracking and the catalytic reactions, and the interactions between the two catalyst components of the hybrid catalyst, resulted in maximum production of light olefins when the hybrid catalyst contained 40 wt% of zeolite. The main chemical links between the thermal cracking (TC) and the catalytic reactions were the conversions of diolefins and large olefins, the latter being produced by the TC and the active sites of the chromium-bearing cocatalyst, respectively.     

Structure Characteristics and NO Selective Catalytic Reduction Property of Sn x Zr1-x O2 Solid Solution Catalysts

Novel catalysts, Sn_xZr_1-xO₂ solid solutions, for NO selective catalytic reduction:NO SCR) are reported. They have much higher activity and selectivity than SnO₂ and ZrO₂. Sn⁴⁺ is the main reductive sites as proved by TPR. The dilution of Sn sites by the coexisting Zr causes a suppression of propene combustion and consequently promoted the selective reduction of NO. The rutile structure might be beneficial to NO SCR.     

Highly Active Au/TiO2 Catalysts for Low-Temperature CO Oxidation: Preparation, Conditioning and Stability

Using a modified depositionprecipitation procedure and a new reductive conditioning method, Au/TiO₂ catalysts with small metallic Au particles (<2 nm) and a very high activity for low-temperature CO oxidation were prepared. The particles are stable during reaction; a decreasing activity is caused by the accumulation of by-products on the catalyst.