Effect of alkyl nitrite decomposition on catalytic performance of CO coupling reaction over supported palladium catalyst

The syntheses of dimethyl oxalate (DMO) and diethyl oxalate (DEO) by CO coupling reaction in gaseous phase were investigated in a fixed bed reactor over Pd-Fe/Al₂O₃ catalyst. The catalytic performance was characterized by CO conversion, space-time yield (STY) and selectivity of DMO (or DEO). The results showed that over Pd-Fe/Al₂O₃ catalyst, the STY of DMO was higher than that of DEO under the same reaction conditions. The optimum reaction temperatures for synthesizing DMO and DEO were 403 K and 393 K, respectively, at the molar ratio 1 ∶ 1 of alkyl nitrite to CO. The difference in synthesizing DMO and DEO on the same catalyst was attributed to the decomposition performances of methyl nitrite (MN) and ethyl nitrite (EN), as density functional theory (DFT) calculation showed that EN decomposed more easily than MN.     

半焦炭催化甲烷裂解及动力学特性

在平推流反应器上,考察了非催化和半焦炭催化条件下甲烷裂解.利用气相色谱分析研究了甲烷裂解的规律.结果表明,半焦对甲烷裂解具有明显的催化作用,不同种类的炭催化剂表现出相似的催化活性.半焦炭催化剂条件下,甲烷裂解转化率同时受两方面的影响:一方面甲烷裂解产牛的积炭沉积在半焦表面及孔内,覆盖大部分的活性位,同时堵塞半焦内的孔道阻碍甲烷向半焦孔内扩散,使甲烷的裂解率降低;另一方面甲烷裂解生成的新物种反过来又对甲烷的裂解起催化作用,促进甲烷裂解.研究还表明,半焦中的灰分对甲烷裂解没有明显的作用,甲烷裂解主要受温度控制.采用简单的平推流模型对甲烷热分解动力学参数进行了计算,计算得到甲烷非催化和半焦催化裂解的表观活化能分别为154.02 kJ/mol和82.06 kJ/mol.     

钯复合材料电极催化甲醇氧化机理

在NaY/Teflon修饰玻碳电极上电化学辅助沉积钯微粒,制备钯复合材料电极,研究催化反应机理。采用循环伏安法(CV)、计时电流法和扫描电镜进行表征,结果表明,钯复合材料电极对甲醇的催化是单电子过程,改变甲醇氧化途径,降低活化能。该电极具有优越的放电特性,提高甲醇和电极利用率,对甲醇氧化具有良好的电催化活性。     

Pd-Co/CNT复合催化剂的制备及甲醇电氧化性能

以Pd Cl₂和Co(NO₃)₂为原料，采用分步乙二醇还原法制备了多壁碳纳米管负载Pd-Co复合纳米催化剂Pd-Co/CNT。利用TEM、XRD和XPS对催化剂的结构进行了表征，考察了其甲醇电氧化性能。结果显示，Co的引入使Pd催化剂的分散性得到改善，其电化学表面积可达39.7 m²/g。循环伏安测试表明，当Pd∶Co物质的量比为1∶0.2时，Pd-Co/CNT的甲醇氧化峰电流密度约为Pd/CNT的2.7倍。计时电流结果表明，Co的添加使催化剂的活性衰减比例由Pd/CNT的63.8%降至54.2%，显示出较强的抗中毒能力。Pd-Co复合催化剂性能的改善归因于Pd与Co之间的协同相互作用。     

丙烯选择性催化还原NO的钯催化剂的理论研究

采用密度泛函理论（DFT）方法在B3LYP／lanl2dz水平上，选择金属钯（111）晶面上的单个Pd原子作为催化剂活化中心，对丙烯在金属钯上选择性催化还原N0的反应机理进行了理论研究，计算了反应物、过渡态、产物的几何构型和反应势垒，并通过振动分析和内禀反应坐标（IRC）对过渡态加以确认，完整地给出了反应沿极小能量途径的变化过程。结果表明，活化势垒太高，反应很难进行，所以单个钯原子不具有催化活性。     

甲醇在Fe/MgO、Co/MgO和Ni/MgO催化剂上裂解制备氢气

采用浸渍法制备出3种MgO负载型过渡金属催化剂Fe/MgO、Co/MgO和Ni/MgO,系统研究了甲醇在3种催化剂上于600℃下的裂解产物。结果表明,3种催化剂均能催化甲醇裂解产生富氢气体,同时产生碳纳米管。其中,Ni/MgO具有最佳的催化效果。     

钯催化交叉偶联反应催化剂的研究进展

钯催化交叉偶联反应是一类用于碳碳键形成的重要反应 ,在有机合成中应用十分广泛。着重综述了几种常用的钯催化交叉偶联反应催化剂研究的一些新进展     

甲醇气体的电晕放电分解特性模拟

分别用2种内径、4种长度的黄铜圆管作为正极,2种直径的电晕线作为负极构成电晕放电反应器,分解去除低体积分数甲醇气体。去除率随电流密度的增加而上升,随入口甲醇体积分数的增高和气体流速的增大而降低。考察反应和传质对过程的共同影响,建立了描述反应器内甲醇和臭氧体积分数变化的数学模型。模型在多种反应器长度和内径、电晕线直径等装置条件,以及多种电流密度、入口甲醇体积分数、气体流速等操作条件下,预测结果的平均相对误差小于6.4%。本研究量化了甲醇电晕放电分解的过程变化,可作为反应器的设计和运行控制的依据。     

钯催化芳基硼酸与芳卤偶联反应的工业应用新进展

钯催化芳基硼酸与芳卤偶联反应(即Suzuki反应)是用于碳碳键形成的重要方法之一,在有机合成中应用十分广泛。本文着重综述了钯催化Suzuki偶联反应在工业化应用方面的一些新进展。     

NC306型铜基甲醇合成催化剂宏观动力学研究C

采用磁力搅拌内循环无梯度反应器在 5MPa、 2 30～ 2 70℃和气体组成 (摩尔分率 ) CO0 .0 391～ 0 .1 72 3,CO2 0 .0 0 55～ 0 .1 2 38,H2 0 .5840～ 0 .7349(余为 N2 和 CH4 )条件下 ,对国产 NC30 6型铜基甲醇合成催化剂的低压宏观动力学特性进行了实验研究。基于 CO、CO2 竞争加氢双路线合成甲醇反应模式 ,以 Simplex- Powell复合法对实验数据进行搜索、寻优 ,建立了 NC30 6催化剂的宏观动力学模型。统计检验结果表明 ,所建模型良好地吻合了实验结果 ,是适宜和可信的。     

聚苯乙烯负载二环己胺钯催化Heck反应的研究

以聚苯乙烯树脂为载体、二环己胺为配体制备聚苯乙烯负载胺钯催化剂。采用XPS、XRD、TG、DTA和SEM等方法对其进行表征,针对不同催化体系探讨丙烯酸、苯乙烯与芳基碘的Heck反应的催化性能。结果表明,高分子胺配体与钯之间形成配位作用,制备的催化剂在室温～200 ℃有较好的热稳定性。该负载型催化剂在N₂氛围只需少量的催化剂就能较好地催化丙烯酸、苯乙烯与芳基碘的Heck反应,较高收率地生成取代的反式肉桂酸和1,2-二苯基乙烯。     

First-principles analysis of the hydrogenation of carbon monoxide over palladium

The reaction paths for the hydrogenation of CO to methanol over Pd_x (x = 1–4 and 19) cluster models were examined using first-principle density functional quantum chemical calculations. The predicted adsorption energies for the most favorable binding modes for CO, H₂, HCO, H₃CO, CH₃OH, C, O and H on a Pd₁₉ model Pd(111) clusters were -147, -62, -340, -51, -195, -33, -610, -349 and -251 kJ/mol, respectively. The most favorable modes for CO, CH₃O, H, C and O on Pd(111) were all found to be the 3-fold fcc site. The most favorable modes for the formyl and formaldehyde surface intermediates at low coverage were the 3-fold (ζ²μ³), and the di-σ sites, respectively. At higher surface coverages, however, the atop ζ¹ (C) and the π modes for the formyl and formaldehyde intermediates were more likely. The computed adsorption energies were subsequently used to compute overall reaction energies for the hydrogenation of CO to methanol. The initial hydrogenation of CO to the ζ¹ (C) HCO intermediate was found to be +52 kJ/mol endothermic and has been speculated as a possible rate-limiting step. The remaining surface hydrogenation steps become increasingly more exothermic as more hydrogen was added. The elementary steps of formyl to formaldehyde, formaldehyde to methoxide and methoxide to methanol were computed to be -9, -26 and -33 kJ/mol, respectively. The overall energy for CO dissociation was found to be highly unlikely at +260 kJ/mol and a clear indication that methanation and chain growth chemistry is not very likely over Pd. The most favorable reaction coordinate for the hydrogenation of CO to the ζ¹ (C) formyl intermediate was that which proceeds over a single Pd site where there is a migratory insertion of the CO into a Pd–H bond. The barrier for this path was computed to be +78 kJ/mol on the Pd₁₉ cluster. There was a very weak dependence on cluster size. This is a likely indication that this reaction is structure insensitive. A second path which involved the coupling of H and CO over a bridge site was found to be +130 kJ/mol which is less likely, but may also occur under different conditions. This revised version was published online in June 2006 with corrections to the Cover Date.     

甲醇裂解制氢工艺安全评价研究

以中等规模8 400 m3/h甲醇裂解制氢项目为例,采用道化学火灾爆炸危险指数法对其安全问题进行量化研究,并通过采取安全措施使其危险性由"非常大"下降为"中等"。     

甲醇制汽油反应机理探讨

介绍了发展甲醇制汽油技术的必要性及应用前景。分析了目前煤制汽油的3种方法,即,煤直接液化制备汽油、煤间接液化合成汽油、煤经过中间产品(甲醇)制备汽油,并对3种方法的优劣进行了简单的比较。主要从甲醇制汽油反应历程、甲醇脱水形成二甲醚机理、催化剂上C1物种相互结合形成C—C键的机理3方面对甲醇制汽油的机理进行了探讨。     

Mechanism of methanol decomposition on the Pd/WC(0001) surface unveiled by first-principles calculations

In this study, the decomposition of methanol into the CO and H species on the Pd/tungsten carbide (WC)(0001) surface is systematically investigated using periodic density functional theory (DFT) calculations. The possible reaction pathways and intermediates are determined. The results reveal that saturated molecules, i.e., methanol and formaldehyde, adsorb weakly on the Pd/ WC(0001) surface. Both CO and H prefer three-fold sites, with adsorption energies of −1.51 and −2.67 eV, respectively. On the other hand, CH₃O stably binds at three-fold and bridge sites, with an adsorption energy of −2.58 eV. However, most of the other intermediates tend to adsorb to the surface with the carbon and oxygen atoms in their sp³ and hydroxyl-like configurations, respectively. Hence, the C atom of CH₂OH preferentially attaches to the top sites, CHOH and CH₂O adsorb at the bridge sites, while COH and CHO occupy the three-fold sites. The DFT calculations indicate that the rupture of the initial C–H bond promotes the decomposition of CH₃OH and CH₂OH, whereas in the case of CHOH, O–H bond scission is favored over the C–H bond rupture. Thus, the most probable methanol decomposition pathway on the Pd/WC(0001) surface is CH₃OH → CH₂OH → trans-CHOH → CHO → CO. The present study demonstrates that the synergistic effect of WC (as carrier) and Pd (as catalyst) alters the CH₃OH decomposition pathway and reduces the noble metal utilization.     

In situ ellipsometric study of a palladium catalyst during the oxidation of methane

Ellipsometry is used to follow the growth of a PdO layer on the surface of a thick Pd-film catalyst during methane oxidation at 500°C. The oxide layer that develops under rich conditions (excess CH₄) is quite porous and roughens with time. Little CO is formed during this period, but the CO₂ formation rate increases until spontaneous oscillations develop, which correlate with changes in the ellipsometric data. These changes indicate that the porous oxide rapidly converts to a metal-rich state, which has decreased catalytic activity, and then slowly reoxidizes.     

HZSM-5分子筛上吸附苯和甲醇的TPSR-MS研究

对不同硅铝比HZSM-5分子筛进行程序升温表面反应-质谱(TPSR-MS)实验和原位程序升温氧化(TPO)。结果表明,苯在HZSM-5分子筛上于60℃下吸附后程序升温脱附的过程中检测到乙烯,硅铝比越低,检测到的乙烯越多,HZSM-5分子筛上的残碳量越大。甲醇在HZSM-5分子筛上于60℃下吸附后程序升温脱附的过程中检测到甲苯,但未检测到苯,硅铝比越低,检测到的甲苯量越大;同时检测到氢气,硅铝比越低,氢气量越小,TPO检测到的残炭量越小。吸附温度越高,甲醇越易转化成甲苯。     

ＬＣ３０８型合成甲醇催化剂的实验室研究

对新工艺制备的ＬＣ３０８型合成甲醇催化剂进行了实验室研究,讨论了反应条件对催化剂性能的影响,其性能较目前工业使用的同类催化剂有明显的改进,提高了催化剂的活性和热稳定性。     

Mechanistic aspects of methanol oxidation on platinum-based electrocatalysts

An understanding of the overall mechanism of the electrooxidation of methanol is of considerable interest in relation to the optimization of the direct methanol fuel cell. This paper describes in detail the different steps in the oxidation of methanol on platinum-based electrocatalysts with the identification of the key adsorption steps and of the different intermediates involved. From these fundamental studies, it is shown how it is possible to design multimetallic electrocatalysts for the electrooxidation of methanol under experimental conditions suitable for fuel cell application.     

Highly enantioselective hydrogenation of α-Alkyl-β-arylpropenoic acids over cinchonidine-modified palladium catalyst

Enantioselective hydrogenation of (E)- α-alkyl-β-arylpropenoic acids was studied over the cinchonidine-modified Pd/C under the conditions optimized for (E)-α,β-diarylpropenoic acids. Enantiomeric excess (ee) of the product was increased by adjusting the α-alkyl group as a properly bulky isopropyl. The ee was as high as 80% when the β-group is phenyl, and reached 86% with p-anisyl group. Stereoselection of those substrates is similar to that of (E)-α,β-diarylpropenoic acids.