Bi-Pt催化剂在H-mordenite载体上的甘油选择性氧化

以Bi-Pt/H-mordenite为催化剂,对甘油(GLY,Glycerol)选择性氧化制备二羟基丙酮(DHA,Dihydroxyacetone)进行了研究。采用BET对催化剂进行表征,结果表明,催化剂的比表面积对催化剂的反应性能影响较小。甘油的裂解是主要的副反应,而H-mordenite可以抑制甘油的裂解,提高DHA的选择性。最佳反应条件为温度353 K,反应时间2～4 h,空气流量20 mL/min,甘油(水-乙醇1:1混合溶液的质量分数为10%),催化剂为1%Bi-5%Pt/H-mordenite时,甘油的转化率为70.6%,DHA的选择性为61.0%。

Spacial hindrance induced recovery of over-poisoned active acid sites in pyridine-modified H-mordenite for dimethyl ether carbonylation

Zeolite catalysts,such as H-mordenite(H-MOR),are readily deactivated by coke deposition in carbonylation reactions.Pyridine modification of H-MOR can improve its stability but can lead to an undesirable loss in catalytic activity.Herein,we report the intrinsic impact of the pyridine adsorption behavior on H-MOR and the spacial hindrance of the zeolite frameworks on dimethyl ether(DME)carbonylation at a molecular level.We discovered that acid sites at O2 positions,located on common walls of eight-membered ring(8-MR)side pockets and 12-MR channels,were active in DME carbonylation,but were unfortunately poisoned during pyridine modification.Density functional theory calculations revealed that the pyridine-poisoned acid sites at the O2 positions could be easily regenerated due to the spacial hindrance of the zeolite frameworks.Accordingly,they can be facilely regenerated by proper thermal treatment,which induces 60%promotion in the catalytic activity along with a high stability.Our findings demonstrate the determining role of O2 positions in H-MOR for DME carbonylation and provide a new avenue for the rational design of other efficient zeolite-relevant catalytic systems.

Tert-butylation of Toluene with Tert-butyl Alcohol over Realuminated H-mordenite Zeolite

The realuminated H-mordenite catalysts （HM1-4） treated with different concentrations of NaOH and NaAlO2 aqueous solutions were prepared, and characterized by inductively coupled plasma （ICP）, X-ray diffraction （XRD）, Fourier transform-infrared spectroscopy （FT-IR） and temperature-programmed desorption of ammonia, They are of lower Si/AI ratio and higher acid amount while keeping a high relative crystallinity. Their catalytic performances were evaluated with the liquid-phase tert-butylation of toluene with tert-butyl alcohol in a 100 ml stainless steel batch reactor equipped with a stirrer. HM2 zeolite catalyst, obtained by treating HM in 0.1 mol.L-1 NaOH followed by 0.05 mol·L^-1 NaAlO2 aqueous solution, shows a higher catalytic activity because of its highest acid amount. For HM2 catalyst the influences of reaction conditions on catalytic performance were investigated. The conversion of toluene is 50.3% and the selectivity ofp-tert-butyltoluene is 74.7% at a temperature of 180℃, 2 of molar ratio of tert-butyl alcohol to toluene, 4h of reaction time and 0.2 of M（catalyst）/M（toluene）.

Phenol Tert-Butylation Catalyzed by Zeolite H-Mordenite

Para-tert-butyl phenol (p-TBP) and 2,4-di-tert-butyl phenol (2,4-DTBP) are widely used for the preparation of antioxidants. Zeolite catalysts showed good performance for the synthesis of p-TBP and 2,4-DTBP. In this work, zeolite H-mordenite (HM) catalyst was prepared and the alkylation of phenol with tert-butyl alcohol over zeolite HM catalyst was investigated at different reaction conditions. It is found that increasing temperature enhances the selectivity to p-TBP and the optimum reaction temperature for phenol conversion is 438 K. Increasing flow rate decreases phenol conversion apparently while the selectivity to p-TBP has a little increase. The suitable tert-butyl alcohol/phenol molar ratio is 2. Lower alcohol/phenol molar ratios are beneficial to p-TBP while higher ones are helpful for producing 2,4-DTBP.

Highly selective hydration reaction of a-pinene over H-mordenites pretreated with quaternary ammonium salts

The application of shape-selectivity of zeolite in petrochemistry has been an ac-tive research area since it was first proposed by Weisz and Frilette, and the tendencyto utilize the potential for specific, highly selective syntheses in the field of inter-mediates and fine chemicals has continued steadily in recent years. Nevertheless,

Modifying the acidity of H-MOR and its catalytic carbonylation of dimethyl ether

Among the reactions catalyzed by zeolites there are some that exhibit high selectivity due to the spatial confinement effect of the zeolite framework.Tailoring the acidity,particularly the distribution and location of the Bronsted acid sites in the zeolite is effective for making it a better catalyst for these reactions.We prepared a series of H-mordenite（H-MOR） samples by varying the composition of the sol-gel,using different structure directing agents and post-treatment.NH3-TPD and IR characterization of adsorbed pyridine were employed to determine the amount of Bronsted acid sites in the 8-membered ring and 12-membered ring channels.It was shown that controlled synthesis was a promising approach to improve the concentration of Bronsted acid sites in MOR,even with a low Al content.Using an appropriate composition of Si and Al in the sol-gel favored a higher proportion of Bronsted acid sites in the 8-membered ring channels.HMI as a structure-direct agent gave an obvious enrichment of Bronsted acid sites in the 8-membered ring.Carbonylation of dimethyl ether was used as a probe reaction to examine the modification of the acid properties,especially the Bronsted acid sites in the 8-membered ring channels.There was a linear relationship between methyl acetate formation and the number of Bronsted acid sites in the 8-membered ring channels,demonstrating the successful modification of acid properties.Our results provide information for the rational design and modification of zeolites with spatial constraints.

Halide-free carbonylation of methanol with H-MOR supported CuCeO_(x) catalysts

Heterogeneous halide-free carbonylation of methanol to acetates,including methyl acetate(MA)and acetic acid,using non-precious metal catalysts has been a topic of interest for decades.The key issue is that the water produced by methanol dehydration inhibits the formation of acetyl species and reduces the MA selectivity.Here,we report that CuCeO_(x)/H-mordenite(H-MOR)catalyst can nearly eliminate the inhibiting effect of water on carbonylation by a water-gas shift reaction(WGSR)on-site,and can thus achieve 96.5%methanol conversion with 87.4%MA selectivity for the halide-free carbonylation of methanol.The results of powder X-ray diffraction,transmission electron microscopy,and scanning electron microscopy show that the Cu and Ce species are highly dispersed on H-MOR even when the CuCeO_(x)contents are as high as 29 wt-%.Fourier transform infrared spectroscopy and CO chemisorption analysis reveal that a small portion of Cu species can migrate into the channel of H-MOR when CuCeO_(x)/H-MOR is calcined at 500℃and these Cu species are converted into Cu^(+) sites upon reduction.The Cu^(+) sites facilitate the WGSR and are also active sites for methanol carbonylation.The introduction of Ce benefits the inhibition of coke deposits and thus enhances the catalyst stability.