含氯挥发性有机物的催化氧化研究进展

催化氧化是控制挥发性有机污染物排放的有效途径之一,但传统催化剂在氧化消除含氯挥发性有机物(CVOCs)时易中毒而失活,因此,研发新型、高效、稳定的催化剂对其工业应用具有重要意义。简要综述近年来稀土及过渡金属氧化物、分子筛和负载贵金属催化剂对CVOCs氧化的催化性能和催化反应机理,剖析CVOCs氧化反应副产物的形成和催化剂失活的原因,并展望CVOCs催化氧化技术的未来发展趋势。     

甲醇气相脱水制二甲醚催化剂研究进展

甲醇气相脱水制二甲醚反应为固体酸催化反应,常用的固体酸催化剂有γ-Al₂O₃和分子筛类。γ-Al₂O₃表面存在弱酸中心或中等强度酸中心,催化剂有较好的初始催化活性,但活化所需的反应温度较高,耐水稳定性差;分子筛类催化剂表面有许多强酸性位,低温下催化活性较高,但在高温反应条件下易产生烃类副产物和积炭,热稳定性差。为改善这两类催化剂的催化性能,对催化剂进行了各种改性研究,改性后催化剂的活性、选择性和稳定性均有一定程度提高。综述了近年来在γ-Al₂O₃和分子筛催化剂上进行的改性研究,总结并展望了甲醇脱水催化剂的发展方向。     

模板剂对ZSM-5分子筛甲醛环化制三聚甲醛性能的影响

以四丙基氢氧化铵、四丙基溴化铵、正丁胺和季戊四醇为模板剂水热合成ZSM-5分子筛，采用XRF、XRD、SEM、NH₃-TPD、Py-FTIR和²⁷Al MAS NMR等进行了表征，研究了模板剂对ZSM-5分子筛性质及甲醛制三聚甲醛催化性能的影响。结果表明，通过改变模板剂可改变ZSM-5分子筛的酸中心分布、表面酸性质和粒径；较大空间的孔道交叉位置的酸性中心、小催化剂粒径和高表面B酸/L酸比值有利于提高三聚甲醛选择性。以四丙基氢氧化铵为模板剂合成的ZSM-5分子筛的颗粒尺寸为240nm×240nm×150nm，分布于直形孔道和S形孔道的孔道交叉处的Br?nsted酸中心较多，甲醛转化率和三聚甲醛的选择性分别为30.15%和88.35%。     

TPAOH-NH_3·H_2O溶液处理TS-1/SiO_2对丙烯环氧化反应影响

将SiO_2负载的钛硅分子筛(TS-1/SiO_2)用四丙基氢氧化铵和氨水混合溶液处理并用于催化丙烯环氧化制环氧丙烷反应。结果表明,混合溶液处理的钛硅分子筛比用四丙基氢氧化铵或氨水单独处理的样品具有更好的催化性能。随着混合碱中氨水浓度从0.01 mol·L-1增加到0.03 mol·L-1,附着在分子筛表面的二氧化硅载体消失,可能被溶解并再结晶到分子筛表面。同时,在此溶解再结晶过程中,分子筛内部产生许多介孔,使其催化性能显著提升,而二氧化硅表面酸性位被消除。四丙基氢氧化铵和氨水协同作用产生大的介孔,有利于高分子量副产物扩散出催化剂粒子,导致催化剂稳定性明显提升而催化活性和选择性不受影响。     

La修饰ZSM-5分子筛催化剂用于C4烯烃催化裂解制丙烯

采用不同含量的La对ZSM-5分子筛进行改性，考察其在C₄烯烃催化裂解制丙烯反应中的催化性能。结果发现，少量La的引入不会破坏分子筛催化剂的骨架结构，改性后催化剂活性的变化是由于其表面酸性的改变而引起。分子筛催化剂表面酸量决定其C₄烯烃裂解反应活性，La的加入使催化剂表面酸量减少，从而使烯烃转化率降低。催化剂表面酸强度是影响其产物分布的主要因素，酸性越强，催化剂裂解能力越强，产物丙烯的选择性也就越高。尽可能提高催化剂表面强酸的酸量是C₄烯烃催化裂解制丙烯反应催化剂的研制方向。     

HCl催化氧化制Cl_2的Cu-Ce混合氧化物催化剂研究

分别采用体相模板法和表面模板法制备了铜改性Ce O_2催化剂(Cu O-Ce O_2和Cu O/Ce O_2)。利用XRD、N2吸附-脱附、Raman、H2-TPR对催化剂进行了表征并考察了其催化氧化HCl制Cl2的性能。结果表明:体相模板法更有利于制备铜物种分散度更高的催化剂,提高催化剂表面氧空位的浓度。将催化剂表面氧空位浓度与HCl催化氧化活性关联发现,催化剂氧空位浓度是影响HCl催化氧化活性的重要因素。酸洗前后催化剂催化活性对比表明,高分散的Cu O在较低温度时对催化剂活性贡献不大,而在较高温度时可以有效促进催化剂催化性能。晶相Cu O对HCl的催化氧化活性没有贡献。     

丁烯催化裂解制取丙烯催化剂的研究进展

丁烯催化裂解制丙烯是提高丁烯利用率、提高丙烯生产工艺经济效益的新技术。分析和讨论了丁烯催化裂解制丙烯的反应机理,分别探讨了不同催化剂的优势及不足之处,包括金属氧化物催化剂、分子筛催化剂、复合分子筛催化剂和改性分子筛催化剂等。总结了分子筛酸强度、酸密度及催化剂孔道结构对催化剂转化率、丙烯选择性和稳定性的影响。提出了合成分子筛催化剂的酸性强度及酸密度是分子筛催化剂改性的主要目标,通过分子筛改性,可以提高分子筛催化剂的催化活性及目标产物丙烯的选择性,同时减少结焦,改善催化剂稳定性。最后对用于丁烯裂解制备丙烯催化剂的发展趋势和前景进行了前瞻性点评和展望。     

氟化镁基催化剂催化2-氯-1,1,1,2-四氟丙烷气相脱卤化氢反应性能研究

采用等体积浸渍法制备了不同金属离子(M~(n+))改性的系列氟化镁基催化剂(M/MgF_2),考察了其在高温气相条件下催化转化2-氯-1,1,1,2-四氟丙烷(HCFC-244bb)合成新一代环保制冷剂2,3,3,3-四氟丙烯(HFO-1234yf)的反应性能。实验结果表明,单一氟化镁上同时存在脱HF、脱HCl 2种反应过程,但前者为主反应,脱HF生成副产物2-氯-3,3,3-三氟丙烯(HCFO-1233xf)的选择性达87.7%,目标脱HCl产物HFO-1234yf选择性不足10%。Al~(3+)改性后,催化剂活性显著增加,但脱HF选择性也随之增大(约90%)。3%Fe/MgF_2、3%Zr/MgF_2催化剂上HFO-1234yf选择性有所提高,但不足20%。碱金属K~+、Cs~+的添加可大幅提高催化剂的脱HCl选择性,分别为76.4%和86.6%,但催化剂活性低于未改性MgF_2催化剂。采用N_2物理吸附、NH_3-TPD等表征手段对催化剂结构、表面酸性进行表征,并将其与催化反应性能进行关联,结果表明,催化剂表面酸性的减弱有利于反应向选择性脱HCl方向移动。     

Lewis酸催化合成草酸二苯酯反应研究

研究了Lewis酸催化剂催化苯酚和草酸二甲酯酯交换合成草酸二苯酯(DPO)反应。考察了不同Lewis酸催化剂对DPO合成反应的催化活性和Lewis酸催化剂的酸性对催化性能的影响,确定了弱酸中心促进主产物甲基苯基草酸酯(MPO)和DPO的生成,而强酸中心有利于副产物苯甲醚的生成。以弱酸TS-1分子筛为催化剂,MPO和DPO总选择性为99.2%。以强酸AlCl3为催化剂,苯甲醚选择性达到60.4%。探讨了Lewis酸催化剂催化苯酚和草酸二甲酯酯交换合成草酸二苯酯反应机理。Lewis酸催化苯酚和DMO酯交换合成MPO反应是按酰氧键断裂的反应历程进行的,DMO中和羰基相连的给电子基的-COO-基团及较大的基团体积降低了苯酚和DMO酯交换合成MPO反应的反应活性。而苯酚和DMO甲基化反应生成苯甲醚是按烃氧键断裂的反应历程进行的。     

TPAOH-NH3·H2O溶液处理TS-1/SiO2对丙烯环氧化反应影响

将SiO₂负载的钛硅分子筛(TS-1/SiO₂)用四丙基氢氧化铵和氨水混合溶液处理并用于催化丙烯环氧化制环氧丙烷反应。结果表明,混合溶液处理的钛硅分子筛比用四丙基氢氧化铵或氨水单独处理的样品具有更好的催化性能。随着混合碱中氨水浓度从0.01 mol·L^-1增加到0.03 mol·L^-1,附着在分子筛表面的二氧化硅载体消失,可能被溶解并再结晶到分子筛表面。同时,在此溶解再结晶过程中,分子筛内部产生许多介孔,使其催化性能显著提升,而二氧化硅表面酸性位被消除。四丙基氢氧化铵和氨水协同作用产生大的介孔,有利于高分子量副产物扩散出催化剂粒子,导致催化剂稳定性明显提升而催化活性和选择性不受影响。     

The role of acidity in the decomposition of 1,2-dichlorobenzene over TiO2-based V2O5/WO3 catalysts

The influence of Lewis and Brønsted acid sites on the performance of V₂O₅/TiO₂ and V₂O₅–WO₃/TiO₂ catalysts in the total oxidation of o-dichlorobenzene was investigated. Catalytic activity of these materials resulted strongly affected by their acidic properties. The presence of Brønsted acid sites significantly increases the o-DCB conversion but also leads to the uncompleted degradation of chlorinated compounds, promoting the formation of partial oxidation products, as dichloromaleic anhydride. On the contrary, Lewis acid sites, acting as absorbing sites, promote the further oxidation of intermediates to CO and CO₂, without any by-products desorption.

Furthermore, the presence of water in the feed-stream was proven to decrease o-DCB conversion but also to play a positive role on process selectivity, increasing COx production. Plausible reasons for this effect are the reduction of Brønsted acid sites and the hydrolysis of anhydride during wet tests.     

Effect of Co content on the catalytic activity of CoSiBEA zeolite in the selective catalytic reduction of NO with ethanol: Nature of the cobalt species

The effect of Co content on the catalytic activity of CoSiBEA zeolites in the selective catalytic reduction (SCR) of NO with ethanol is investigated. The Co_xSiBEA zeolites (x = 0.3, 0.7, 3.6 and 6.75 Co wt.%) are prepared by a two-step postsynthesis method which allows to control the introduction of cobalt into zeolite and thus to obtain catalysts with specific Co sites. The nature of the active sites is characterized by XRD, diffuse reflectance UV–vis, H₂-TPR and XPS.

The catalytic activity of Co_xSiBEA strongly depends on the nature and environment of Co species. Zeolites with isolated lattice tetrahedral Co(II) (Co_0.3SiBEA and Co_0.7SiBEA samples) are active in SCR of NO with ethanol with selectivity toward N₂ exceeding 85% for NO conversion from 20 to 70%. When additional isolated extra-lattice octahedral Co(II) species appear (Co_3.6SiBEA sample), the full oxidation of ethanol by dioxygen becomes a very important reaction pathway. In presence of additional cobalt oxides (Co_6.75SiBEA sample), the activity and selectivity toward N₂ substantially change and full oxidation of ethanol to CO₂ is the main reaction pathway and full NO oxidation also takes place in the temperature range 550–775 K. The lack of correlation between the activity in SCR of NO with ethanol and NO oxidation to NO₂ suggests that the two reactions are more competitive than sequential.     

Catalytic decomposition of chlorodifluoromethane (HCFC-22) over platinum supported on TiO2–ZrO2 mixed oxides

Sulfated and non-sulfated TiO₂–ZrO₂ were promoted with platinum and the activity and selectivity of the resulting catalysts for the hydrolytic decomposition chlorodifluoromethane in air was investigated. The addition of platinum reduced the specific surface area of the catalyst slightly and lowered the catalytic activity. On the other hand, the selectivity of the catalysts towards CO₂ formation was much improved. Metallic platinum was formed by the reduction of the platinum precursor with carbon monoxide produced during the hydrolysis of chlorodifluoromethane over the acidic mixed oxide and promoted the oxidation of CO. At the same time, platinum suppressed completely the formation of the fluorinated byproduct CHF₃, possibly by anchoring itself on the active sites responsible for the fluorination reaction. The platinum promoted non-sulfated TiO₂–ZrO₂ was stable and gave more than 90% of CHClF₂ conversion and 95% selectivity to CO₂ for over 60 h.     

Supported base metal catalysts for the preferential oxidation of carbon monoxide in the presence of excess hydrogen (PROX)

Supported base metal catalysts were tested for the preferential oxidation of CO (CO PROX). The catalysts we investigated covered a wide range of transition metals (Co, Cr, Cu, Ni, Zn) supported on oxides with very different acidic, basic and redox properties (MgO, La₂O₃, SiO₂–Al₂O₃, CeO₂, Ce_0.63Zr_0.37O₂). The influence of the metal loading (Cu), the support properties (acidity, basicity, redox, surface area) and the reaction conditions (reaction temperature, feed composition) on the catalyst activity and selectivity was evaluated. The activity of ceria and ceria–zirconia supported copper catalysts was comparable to the performances of noble metal samples classically used for the PROX reaction. In addition, Cu–CeO₂ catalysts showed a practically constant and high selectivity towards CO oxidation in the temperature range of 50–150 °C. Due to the strong synergetic effect between copper and ceria, only a small amount of copper (0.3 wt.%) was necessary to get an active catalyst. The best catalytic performances were obtained for the samples containing 1–3 wt.% copper. The presence of small copper particles in close interaction with the ceria support was shown to be responsible for the enhanced activity. Except for the hydrogen oxidation, no parallel reactions (CO or CO₂ methanation reactions, coking, RWGS) could be detected over these catalysts. Classically, an increase of the oxygen excess led to an increased CO conversion with a simultaneous loss of selectivity towards CO₂. Finally, the presence of CO₂ in the feed negatively affected the catalytic activity. This effect was attributed to the adsorption of CO₂ on the copper sites, probably as CO.     

Highly effective P-modified HZSM-5 catalyst for the cracking of C4 alkanes to produce light olefins

A series of HZSM-5 zeolites modified by different amounts of phosphorus (P/HZSM-5) were prepared. The physicochemical features of P/HZSM-5 catalysts were characterized by means of XRD, BET, NH₃-TPD, FT-IR spectra of adsorbed pyridine, etc., and their performances for the catalytic cracking of the mixed C₄ alkanes to produce light olefins were investigated. The results indicated that phosphorus (P) modification not only modulated the amount of acidic sites and the percentage of weak acidic sites in total acidic sites, but also regulated the acid type, i.e., the ratio of L/B (Lewis acid/Brönsted acid). The introduction of P also altered the basic characteristics of HZSM-5 which was evidenced by CO₂-TPD analysis. Consequently, P modification with suitable amount was favorable for enhancing the selectivity to light olefins, especially to propene. At the temperature of 650 °C, the maximum yields of propene and ethene were achieved 25.6 and 33.9%, which were higher than those over parent HZSM-5 by 7 and 4.5%, respectively. Aromatics yield was found to be decreased with the increasing P loading due to the reduction of strong acid and the formation of new basic site which inhibited the hydrogen transfer reaction. All this indicates that P-modified HZSM-5 zeolites are effective catalysts for the cracking of mixed C₄ alkanes to produce more light olefins.     

金属氧化物催化CO2与甲醇合成碳酸二甲酯的研究进展

CO₂是主要的温室气体。近年来随着工业的大力发展，CO₂的排放量迅猛增加，严重影响着人类的生存环境。将CO₂转化成有价值的化工产品，受到了研究领域的广泛关注。其中将CO₂与产能过剩的甲醇作为原料，生产碳酸二甲酯（DMC），既能减少CO₂排放，又能产生有价值的绿色产品DMC。本文简述了影响CO₂转化的因素，即受热力学限制和CO₂活化困难；重点介绍了具有酸碱活性中心的金属氧化物ZrO₂、CeO₂以及复合金属氧化物催化剂的催化性能和反应机理，并分析了影响催化活性的主要原因：表面酸碱性能决定了催化活性；进一步分析了催化剂表面的酸碱性来源于Lewis酸碱位和Br?nsted酸性位。对于开发高效的金属氧化物催化剂未来的研究方向提出了展望: 通过调控催化剂的晶相和形貌、增加氧空位和羟基官能团、掺杂碱性或者酸性物种来改变催化剂表面的酸碱性，并且向催化系统中添加脱水剂。最后指出了由于CO₂分子的稳定性很难被活化，需进一步深入研究其活化CO₂的机理，提高CO₂的转化率。     

火焰喷雾合成法制备La0.8Sr0.2Mn1-xCuxO3催化氧化CO性能研究

采用火焰喷雾合成法制备了Sr²⁺、Cu²⁺分别取代A、B位的La_0.8Sr_0.2Mn_1-xCu_xO₃ （x=0,0.1,0.2,0.3,0.4）钙钛矿催化剂,并用于CO催化氧化实验,研究了水蒸气和CO₂对催化剂CO氧化活性的影响。对不同取代量La_0.8Sr_0.2Mn_1-xCu_xO₃ 催化剂进行了XRD、SEM、EDS、BET、XPS、H₂-TPR和O₂-TPD等表征测试。结果表明,火焰喷雾合成法制备的钙钛矿催化剂具有良好的钙钛矿相、疏松多孔结构和催化氧化活性。其中,La_0.8Sr_0.2Mn_0.9Cu_0.1O₃分别在119.4℃和133.3℃实现50%和90%的CO转化率。掺杂水蒸气和CO₂会与CO在催化剂表面形成竞争吸附,导致5种催化剂性能衰减,但La_0.8Sr_0.2Mn_0.9Cu_0.1O₃仍能在150.2℃实现90%的CO催化转化,在连续稳定性催化氧化测试中,5种催化剂性能衰减不超过10%。结合上述CO催化氧化实验,火焰喷雾合成法制备的催化剂具有良好的稳定性和催化活性,适合制备高CO催化氧化活性的钙钛矿催化剂。     

酸处理Beta分子筛对十氢萘加氢开环反应影响

研究了酸处理过程对Beta分子筛Br nsted酸和Lewis酸分布及其作为载体催化十氢萘加氢开环反应的影响。采用XRD、BET、XRF、Py-FTIR等表征了不同浓度盐酸处理的分子筛,结果表明,酸处理后Beta分子筛结晶度及孔径无明显变化,比表面积先增加后降低。随盐酸浓度的增加,n（SiO₂）/n（Al₂O₃）增大,总酸量逐渐降低;在盐酸浓度大于0.1 mol/L时,酸处理主要改变了分子筛的B酸位。十氢萘加氢开环反应实验结果表明,B酸位对Beta分子筛催化十氢萘开环反应影响较大,酸性越强越易导致作为载体的Beta分子筛失活。0.1 mol/L盐酸处理得到的催化剂酸性适宜,比表面积最大,活性及开环异构产物的产率最高。     

超声浸渍无机盐改性Hβ分子筛催化合成乙基蒽醌

采用超声浸渍法将无机盐Al₂(SO₄)₃、(NH₄)₂SO₄、Ce(NH₄)₂(NO₃)₆和Fe(NO₃)₃负载于Hβ分子筛上,通过NH₃-TPD、XRD和吡啶-IR对分子筛进行表征,考察改性前后分子筛酸性能和晶相的变化。将改性的Hβ分子筛用于催化乙苯和苯酐合成乙基蒽醌。结果表明,不同无机盐超声浸渍改性分子筛的催化效果差别较大,其中,每克分子筛负载0.2 g的Al₂(SO₄)₃的Alβ分子筛催化效果最好,苯酐转化率为45.67%,乙基蒽醌选择性为50.12%。分子筛的酸性能（包括酸量、酸种类和酸强度）对催化性能影响较大。     

Magnéli phases TinO2n−1 as novel ozonation catalysts for effective mineralization of phenol

Magnéli phases Ti_nO_2n-1 have been demonstrated as promising environmentally friendly materials in advanced oxidation processes. In this study, Magnéli phases Ti_nO_2n-1 have been used as catalysts for the ozonation of phenol in aqueous solution for the first time. The materials exhibited excellent catalytic ozonation activities both in phenol degradation and mineralization. When Ti₄O₇ was added, the reaction rate was six-fold higher than that of with ozone alone, while the total organic carbon removal rate was substantially elevated from around 19.2% to 92%. By virtue of the good chemical stability of the materials, a low metal leaching of less than 0.15 mg·L^-1 could effectively avoid the secondary pollution by metal ions. Radical quenching tests revealed ·O₂^- and ¹O₂ to be active oxygen species for phenol degradation at pH 5. As semiconductor catalysts, Ti_nO_2n-1 materials show electronic transfer capability. Ozone adsorbed at B-acid sites of the catalyst surface can capture an electron from the conversion of Ti(Ⅲ) to Ti(IV), and is thereby broken into the active oxygen species. It was interesting to observe that Ti_nO_2n-1 exhibit better catalytic activity for phenol degradation and mineralization with lower n value. The difference in electrical conductivity can be considered as a major factor for the catalytic performances. More highly conductive catalysts show a faster electron-transfer rate and better catalytic activity. Thus, significant evidences have been obtained for a single-electron-transfer mechanism of catalytic ozonation with Magnéli phases Ti_nO_2n-1.