铜基催化剂还原过程研究综述

铜基催化剂广泛应用于工业生产中,催化剂还原是催化剂生产的最后一道工序,也是工业使用前的第一个步骤,对几种铜基催化剂的还原过程进行综述。铜基催化剂主要应用于CO与H_2合成甲醇和CO低温变换,也可用于CO_2与H_2合成甲醇以及脂肪酯加氢制脂肪醇。铜基催化剂的还原方法主要有液相还原法和气相还原法,其中,气相还原法用途较广。对影响还原的条件(H_2浓度、温度、压力和空速等)及杂质(H_2O、O_2和CO_2等)进行总结,并以甲醇合成催化剂为例对低氢还原法和高氢还原法作了介绍。     

甲醇体系电镀污泥衍生磁性多金属材料催化糠醛加氢转化

以电镀行业废弃物电镀污泥为前体合成磁性多金属催化材料,考察其在甲醇供氢体系生物基糠醛加氢转化制备糠醇和2-甲基呋喃的催化性能。通过X射线衍射(XRD)、液氮吸脱附、NH₃程序升温脱附(NH₃-TPD)、扫描电镜(SEM)等手段对煅烧后电镀污泥进行表征,并研究了煅烧温度和各反应工艺条件对甲醇供氢体系糠醛转化的影响。结果表明,电镀污泥衍生磁性多金属材料均具有强酸性位点和部分介孔结构,以铜组分为主的催化活性中心在反应过程中部分被还原为零价,有助于促进甲醇重整产氢和糠醛加氢转化;以700℃煅烧的电镀污泥为催化剂,在240℃反应2 h以上,糠醛几乎完全转化,产物中糠醇和2-甲基呋喃最高收率(摩尔分数)分别为70.9%和31.9%,反应过程副产物以2-呋喃甲基甲醚和2-(二甲氧基甲基)呋喃为主。此外,基于甲醇重整产氢、铜镍组分原位还原以及糠醛加氢反应之间的耦合作用,推测出甲醇体系电镀污泥衍生磁性多金属材料催化糠醛加氢转化可能的反应机制。     

甲醇体系电镀污泥衍生磁性多金属材料催化糠醛加氢转化

以电镀行业废弃物电镀污泥为前体合成磁性多金属催化材料,考察其在甲醇供氢体系生物基糠醛加氢转化制备糠醇和2-甲基呋喃的催化性能。通过X射线衍射(XRD)、液氮吸脱附、NH₃程序升温脱附(NH₃-TPD)、扫描电镜(SEM)等手段对煅烧后电镀污泥进行表征,并研究了煅烧温度和各反应工艺条件对甲醇供氢体系糠醛转化的影响。结果表明,电镀污泥衍生磁性多金属材料均具有强酸性位点和部分介孔结构,以铜组分为主的催化活性中心在反应过程中部分被还原为零价,有助于促进甲醇重整产氢和糠醛加氢转化;以700℃煅烧的电镀污泥为催化剂,在240℃反应2 h以上,糠醛几乎完全转化,产物中糠醇和2-甲基呋喃最高收率(摩尔分数)分别为70.9%和31.9%,反应过程副产物以2-呋喃甲基甲醚和2-(二甲氧基甲基)呋喃为主。此外,基于甲醇重整产氢、铜镍组分原位还原以及糠醛加氢反应之间的耦合作用,推测出甲醇体系电镀污泥衍生磁性多金属材料催化糠醛加氢转化可能的反应机制。     

甲醇合成催化剂的工艺参数优化及反应机理探讨

对自主研制的甲醇合成催化剂进行工艺参数优化,同时根据实验结果对合成气条件下甲醇合成的反应机理进行探讨。实验采用16通道反应器,考察反应温度和接触时间对合成甲醇反应速率的影响,确定适宜的催化剂工艺条件。结果表明,在较长接触时间下,随着温度的升高,CO转化率、H_2转化率和甲醇相对含量先升高后降低,CO_2转化率降低。在较低温度下,CO_2转化率随接触时间延长基本不变,表明甲醇中碳元素主要来自于CO,而CO_2浓度处于水汽变换反应与加氢形成甲醇反应之间的平衡状态。     

Methane conversion to C2 hydrocarbons and hydrogen in atmospheric non-thermal plasmas generated by different electric discharge techniques

Methane conversion to C₂ hydrocarbons and hydrogen has been investigated in a needle-to-plate reactor by pulsed streamer and pulsed spark discharges and in a wire-to-cylinder dielectric barrier discharge (DBD) reactor by pulsed DC DBD and AC DBD at atmospheric pressure and ambient temperature. In the former two electric discharge processes, acetylene is the dominating C₂ products. Pulsed spark discharges gives the highest acetylene yield (54%) and H₂ yield (51%) with 69% of methane conversion in a pure methane system and at 10 SCCM of flow rate and 12 W of discharge power. In the two DBD processes, ethane is the major C₂ products and pulsed DC DBD provides the highest ethane yield. Of the four electric discharge techniques, ethylene yield is less than 2%. Energy costs for methane conversion, acetylene or ethane (for DBD processes) formation, and H₂ formation increase with methane conversion percentage, and were found to be: in pulsed spark discharges (methane conversion 18–69%), 14–25, 35–65 and 10–17 eV/molecule; in pulsed streamer discharges (methane conversion 19–41%), 17–21, 38–59, and 12–19 eV/molecule; in pulsed DBD (methane conversion 6–13%), 38–57, 137–227 and 47–75 eV/molecule; in AC DBD (methane conversion 5–8%), 116–175, 446–637, and 151–205 eV/molecule, respectively. The immersion of the γ-Al₂O₃ pellets in the pulsed streamer discharges, or in the pulsed DC DBD, or in the AC DBD has a positive effect on increasing methane conversion and C₂ yield.     

介质阻挡放电微等离子体分解二氧化碳研究

二氧化碳既是主要的温室气体之一,也是包含碳和氧的资源,把相对惰性的CO₂转化为易于利用的CO是其利用的方法之一。采用介质阻挡微等离子体反应器通过单变量和正交实验探究了反应器参数(放电区长度、放电间距、介质厚度)和工艺参数(输入功率、放电频率和停留时间)对CO₂分解为CO的转化率和能量效率的影响规律。研究结果表明,影响CO₂转化率的大小顺序依次为：放电间距>放电长度>输入功率≈停留时间>介质厚度>放电频率;输入功率60.0 W、放电频率9.0 kHz和停留时间1.5 s、放电区长度60 mm、放电间距0.5 m、介质厚度1.6 mm时,CO₂的转化率为10.6%,能量效率为4.1%。     

Catalytic upgrading of tarry fuel gases: A kinetic study with model components

As a contribution to the development of a process for catalytic upgrading of tarry fuel gases, e.g. coke-oven gas, the conversion of naphthalene, benzene and methane on a nickel catalyst in the presence of H₂ and H₂O was studied. The experiments were performed in a tubular flow reactor (total pressure: 1.6 bar; residence time with respect to the empty reactor: 0.3 s; temperature: 400-950°C; and particle diameter of catalyst: 1.5 mm). The kinetic data were obtained by systematic variation of the reaction conditions.

At temperatures of more than 800°C, each hydrocarbon is cracked and converted with H₂O to CO and H₂. Soot formation does not occur at any temperature. In case of simultaneous conversion of all three hydrocarbons, competitive reactions have to be considered.

The rate of chemical reaction on the catalyst is substantially decreased in the presence of H₂S. Nevertheless, in a reactor of industrial scale, H₂S has only slight influence. The catalyst would be applied with a particle diameter of 19 mm (experiments: 1.5 mm), and the overall reaction rate of hydrocarbon conversion is significantly affected by gas film diffusion.     

Ignition of methanol partial oxidation over supported platinum catalyst

Supported platinum catalysts were prepared by precipitation of H₂PtCl₆ on powders of different metal oxides. Catalytic activity of the prepared catalysts was tested with reaction of partial oxidation of methanol (POM) for hydrogen production. Most of the prepared catalysts can ignite POM at the ambient temperature. The conversion of methanol and the selectivity of hydrogen and carbon monoxide, however, increased with the reaction temperature and varied with the kind of support and platinum loading. A 1 wt% Pt/ZnO catalyst exhibited optimized methanol conversion and selectivity at a low reaction temperature of 150 °C. The reactor may reach this temperature within 2 min after a start of the exothermic reaction.     

木炭水蒸气催化气化制取合成气

以木炭为原料,选用KOH、K₂CO₃、KHCO₃、KNO₃为催化剂,在上吸式固定床气化炉中,进行水蒸气催化气化制取合成气实验。考察了不同催化剂、催化剂用量、水蒸气流量、气化温度对木炭水蒸气气化的炭转化率、产氢率、气体组成体积分数和H₂/CO值的影响。实验通过炭吸收催化剂溶液来负载催化剂,实验结果表明：4种催化剂都可提高木炭气化效率,在浸渍相同质量分数的催化剂溶液下,催化活性顺序为KOH>K₂CO₃>KHCO₃>KNO₃。碳转化率及产氢率都随着催化剂溶液浓度的增加而增大,但浓度过高增加趋势逐渐变缓,催化剂溶液质量分数在4%~6%较为合适。增加水蒸气流量,气体产物中H₂体积分数增大,H₂/CO值增大。升高温度可促进炭气化反应,950℃时碳转化率和产氢率分别达到98.7%和145.23g/kg。实验可得到H₂/CO比1.53~4.09范围间的合成气,可用于合成甲醇、甲烷、二甲醚等燃料。     

Catalytic combustion of natural gas as the role of on-site heat supply in rapid catalytic CO2---H2O reforming of methane

Development in highly active catalysts for the reforming of methane with H₂O, CO₂, and H₂O+CO₂, and partial oxidation of methane was conducted to produce hydrogen with high reaction rates. A Ni-based three-component catalyst such as Ni---La₂O₃---Ru or Ni---Ce₂O₃---Pt supported on alumina wash-coated ceramic fiber in a plate shape was very suitable for both reactions. The catalyst composition was set at 10 wt.-% Ni, 5.6 wt.-% La₂0₃, and 0.57 wt.-% Ru for example, or molar ratios of these components were 1:0.2:0.03. Even with such a low concentration, the precious metal enhanced the reaction rate markedly, and this synergistic effect was ascribed to the hydrogen spillover effect through the part of precious metal and it resulted in a more reduced surface of the main catalyst component. In particular, a marked enhancement in the reaction rate of CO₂-reforming of methane was observed by the modification of a low concentration Rh to the Ni---Ce₂0₃---Pt catalyst. Very high space-time yields of H₂ (i.e., 8300 mol/1 h in partial oxidation of methane at 600°C with a methane conversion of 37.5%, and 3585 mol/1 h in CO₂reforming of methane at 600°C with a methane conversion of 58%) were realized in those reactions. By combining the catalytic combustion reaction, methane conversion to syngas was markedly enhanced, and even with a very short contact time (10 ms) the conversion of methane increased more than that at 50 ms. The space-time yield of hydrogen amounted to 2,780 mol/1 h with a methane conversion of 90% at 700°C. Furthermore, in a reaction of CH₄---CO₂---H₂O---O₂ on the four components catalyst, an extraordinarily high space-time yield of hydrogen, 12 190 mol/1 h, could be realized under the conditions of very high space velocity (5 ms).     

Hydrogenation of silicon tetrachloride in microwave plasma简

This study investigated the hydrogenation of silicon tetrachloride （SIC14） in microwave plasma. A new launcher of argon （Ar） and hydrogen （Ha） plasma was introduced to produce a non-thermodynamic equilibrium activation plasma. The plasma state exhibited a characteristic temperature related to the equilibrium constant, which was termed ＂Reactive Temperature＂ in this study. Thus, the hydrogenation of SIC14 in the plasma could easily be handled with high conversion ratio and very high selectivity to trichlorosilane （SiHC13）. The effects of SiC14/Ar and H2/Ar ratios on the conversion were also investigated using a mathematical model developed to determine the op- timum experimental parameters. The highest hydrogenation conversion ratio was produced at a H2/SiCl4 molar ratio of 1, with mixtures of SICl4 and H2 to Ar molar ratio of 1.2 to 1.4. In this plasma, the special system pressure and incident power were required for the highest energy efficiency of hydrogenating SIC14, while the optimum system pressure varies from 26.6 to 40 kPa depending on input power, and the optimum feed gas （He and SiCI4） molar en- ergy input was about 350 kJ. mo1-1.     

不同反应器中氧化反应与水蒸气气化反应协同作用差异性

在?80mm×3000mm气流床和?40mm×200mm流化床中进行了O₂、H₂O、H₂O+O₂气氛下800℃胜利褐煤气化实验，同时在流化床中进行了O₂、H₂O、H₂O+O₂气氛下半焦原位气化实验和H₂O气氛下半焦完全气化实验。比较了2种反应器中氧化反应与水蒸气气化反应协同作用的大小（强弱）；结合实验条件利用缩核模型分别推导了2种反应器中协同作用影响下水蒸气气化反应速率方程；同时，从传质（扩散）速率、动力学、半焦-挥发分相互作用3方面探讨了2种反应器中协同作用存在显著差异的原因。结果发现，气流床中H₂O+O₂气氛下褐煤转化率明显大于H₂O和O₂单独气氛下褐煤转化率之和，其差值稳定在2.11%～4.01%，而在流化床中差值仅为0～0.75%，相对流化床，气流床中协同作用更明显。这是由于，在流化床中水蒸气向炭粒表面扩散的传质速率约为气流床的11%～25%，水蒸气气化过程受气膜扩散控制，炭粒表面水蒸气全部参与气化反应，炭粒表面无“多余”水分子，氧气开孔/扩孔作用提供的活性位“闲置”，而气流床中气化反应为速控步，炭粒表面有“富裕”水分子，可充分利用氧气开孔/扩孔作用提供的活性位，促进作用显著；挥发分-半焦相互作用不是流化床反应器中协同作用不显著的原因。     

六西格玛方法在Pt/SAPO-11加氢异构催化剂评价反应中的应用

以Pt/SAPO-11为催化剂、正十六烷为模型化合物,进行加氢异构性能反应评价。采用六西格玛设计中的实验设计(DOE)及分析方法拟合并研究各评价参数(反应温度、氢气分压、氢气流速和进料速率)对催化性能的影响及交互作用关系。结果表明,升高反应温度对正十六烷的转化有利,增加氢气分压和进料速率均抑制正十六烷的转化,达到相同转化率需要更高的反应温度,而异构十六烷选择性随温度升高呈现降低趋势;氢气流速的变化对正十六烷转化率和异构十六烷选择性影响较小。拟合结果显示,各评价条件对转化率和异构选择性的影响关系类似,反应温度、氢气分压和氢气流速各自为线性关系,但进料速率与反应温度和氢气分压分别有交互作用,且自身存在二次影响关系,因此,进料速率对评价结果呈曲率影响关系。     

稀土复合固体酸催化合成棕榈酸生物柴油的研究

用溶胶凝胶法制备稀土复合固体酸催化剂SO₄^2-/TiO₂/Ce⁴⁺,将其用于棕榈酸与甲醇的加压酯化反应.考察了不同制备条件对催化剂性能的影响,并对其结构进行表征.结果表明,在Ce⁴⁺浓度0.05 mol/L、H₂SO₄浓度1.38 mol/L、煅烧温度450 ℃和煅烧时间3 h的制备条件下,催化剂活性最高.棕榈酸与甲醇的加压酯化反应最佳工艺条件为:醇酸物质的量之比10:1、反应温度110 ℃、反应时间30 min、催化剂用量3%,此时转化率可达到96.33%.催化剂在重复使用4次后,转化率仍在50%以上.     

H4SiW12O40/SiO2催化正丁醛自缩合反应

正丁醛自缩合合成辛烯醛是工业生产辛醇的重要步骤之一。首先考察了3种杂多酸H₃PW₁₂O₄₀、H₄SiW₁₂O₄₀和H₃PMo₁₂O₄₀对正丁醛自缩合反应的催化性能,发现H₄SiW₁₂O₄₀的催化性能最好。其次,利用浸渍法制备了负载型H₄SiW₁₂O₄₀催化剂,考察了载体和制备条件对催化剂性能的影响,确定以SiO₂为载体,H₄SiW₁₂O₄₀负载量为50%（质量分数）,在150℃焙烧2 h的制备条件。探讨了反应条件对催化剂性能的影响,确定了适宜反应条件：催化剂与正丁醛的质量比为0.15,反应温度120℃,反应时间6 h。在此条件下,正丁醛的转化率为90.4%,辛烯醛的选择性为89.2%。通过对催化剂进行ICP-AES分析和XRD表征,发现活性组分流失是造成催化剂稳定性差的主要原因。为减缓H₄SiW₁₂O₄₀的流失,以[emim]BF₄离子液体为模板剂,采用溶胶-凝胶法制备了H₄SiW₁₂O₄₀/SiO₂催化剂,实验结果表明,催化剂稳定性有一定程度的提高。     

Oxalic acid destruction at high concentrations by combined heterogeneous photocatalysis and photo-Fenton processes

Heterogeneous photocatalysis (HP) using UV/TiO₂, photo-Fenton (PF) reaction using UV/Fe/H₂O₂ and the combination UV/TiO₂/Fe/H₂O₂ (HP–PF) were tested as processes to degrade oxalic acid (Ox) at relatively high concentrations (0.032 M). PF reactions were generally more efficient than HP including the reaction in the absence of H₂O₂. Oppositely to previous results (e.g., with EDTA), HP–PF combinations did not result, in the case of oxalate, better techniques for degradation than systems in the absence of TiO₂. The kinetic behavior was not unique and two parameters were taken to evaluate the efficiency of each system: initial rates (R₀) and time to 95% of total mineralization (TOC₉₅). Addition of hydrogen peroxide improves the initial HP reaction rate and reduces TOC₉₅. Addition of Fe³⁺ also affects the reaction parameters but the effect of H₂O₂ seems to be higher, at least under the present conditions. When both H₂O₂ and iron were added simultaneously, the efficiency was higher. The optimal H₂O₂:Ox:Fe molar ratio was established and the results indicated that, at a fixed iron concentration, H₂O₂ increased R₀ until a limit beyond which it did not cause any effect. No intermediates were formed in the reaction, oxalate being degraded directly to CO₂. Analogies and differences with the EDTA system are presented.     

滑动弧放电等离子体法用于二甲醚重整制氢简

Gliding arc gas discharge plasma was used for the generation of hydrogen from steam reforming of dimethyl ether （DME）. A systemic procedure was employed to determine the suitable experimental conditions. It was found that DME conversion first increased up to the maximum and then decreased slightly with the increase of added water and air. The increase of total feed gas flow rate resulted in the decrease of DME conversion and hydrogen yield, but hydrogen energy consumption dropped down to the lowest as total feed gas flow rate increased to 76 ml. min^-1. Larger electrode gap and higher discharge voltage were advantageous. Electrode shape had an important effect on the conversion of DME and production of H2- Among the five electrodes, electrode 2# with valid length of 55 mm and the radian of 34 degrees of the top electrode section was the best option, which enhanced obviously the conversion of DME.     

煤焦在气化合成气中高温气化反应特性

在固定床管式炉反应器中进行了煤焦在H₂O、CO₂、H₂和CO混合气氛中气化特性的实验研究,考察了反应温度、原料气组成和加煤量对产物气组成以及碳转化率的影响。实验结果表明,在各实验条件下,合成气与煤焦反应后CO流量均增加最多,H₂少量增加。煤焦与CO₂的反应受到明显抑制。混合气体通过与煤焦反应可以提高有效气（CO+H₂）的含量,实验条件下反应出口气体中有效气浓度比反应结束时最多提高3.3个百分点。反应速率受气化剂之间的竞争和气化产物的抑制作用较为明显,在1100℃和1300℃时,煤焦在相同气化剂流量的合成气中的最高反应速率分别只有在纯气化剂（水蒸气或CO₂）中最高反应速率的49%和69%。受到多种气体组分之间的相互影响,气体在孔道里的扩散和吸附对反应影响更加显著,随机孔模型可以较好地拟合此类反应,而不考虑孔结构的均相模型和缩芯模型拟合度较差。     

Liquid phase methanol reforming with water over silica supported Pt–Ru catalysts

The mechanism of the liquid phase methanol reforming reaction over silica supported Pt–Ru catalyst was investigated by kinetic studies, employing a pyrex glass reactor with reflux condensers connected to a closed gas circulation system under ambient pressure. The rate of H₂ formation over Pt–Ru/SiO₂ catalysts was more than 20 times faster than that over Pt/SiO₂ catalysts with high selectivity for CO₂ (72.3%), indicating a marked addition effect of Ru. In the case of HCHO–H₂O reaction over Pt–Ru/SiO₂, the H₂ formation rate was five times larger than that in the CH₃OH–H₂O reaction but selectivity to CO₂ was only 4%. On the contrary, in the HCOOCH₃–H₂O and HCOOH–H₂O reactions, both high activity and selectivity were observed over Pt–Ru/SiO₂. These results clearly indicate that the CO₂ formation does not proceed via HCHO decomposition and following water gas shift reaction. We propose the following pathway for liquid phase methanol reforming reaction over Pt–Ru/SiO₂; a partly dehydrogenated methanol (CH₂OH^*) is the initial reaction intermediate, from which H₂ and CO₂ are formed through HCOOCH₃ and HCOOH as the successive reaction intermediates.     

Selective oxidation of cyclopentene with H_2O_2 by using H_3PW_(12)O_(40) and TBAB as a phase transfer catalyst

The selective oxidation of cyclopentene by aqueous H_2O_2 using H_3PW_(12)O_(40) and tetrabutyl ammonium bromide(TBAB) as a phase transfer catalyst has been investigated. The results show that the presence of TBAB significantly improved the oxidation selectivity of cyclopentene. The effects of the reaction conditions on the conversion of cyclopentene were investigated in detail. The optimal reaction conditions are as follows: the H_3PW_(12)O_(40) to TBAB molar ratio, 1:1–1:3; H_3PW_(12)O_(40) to cyclopentene molar ratio,0.54:100–0.64:100; and molar ratio of H_2O_2 to cyclopentene, 1.6:1. The conversion reached to 59.8% in 4h at 35.0 °C, while the selectivity of glutaraldehyde was 38.0% and the selectivity of 1,2-cyclopentanediol was 55.6%. In addition, a route for oxidation of cyclopentene by aqueous H_2O_2 using a heteropoly acid and quaternary ammonium salt as a phase transfer catalyst was proposed.