Search

Copyright of Journal of Molecular Science is the property of Journal of Molecular Science Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A P-modified Co/SiO2 catalyst was reported for the first time in the selective hydrogenation of dimethyl oxalate (DMO) to methyl glycolate (MG) reaction and the synthesized Co8P/SiO2 exhibited 94.6% conversion of DMO and 88.1% selectivity to MG during a 300 h continuous test. The doping element of P in the catalyst was indispensable and played an important role in improving the catalytic performance of the Co/SiO2 catalyst. [ABSTRACT FROM AUTHOR]

Fe-promoted Co/AC catalysts (15CoxFe/AC) were synthesized by co-impregnation method and studied using CO hydrogenation reaction, N 2 adsorption, ex-situ / in-situ XRD, H 2 -TPR, CO chemisorption and HRTEM. The results showed that the catalytic performance was improved by adding Fe into the 15Co/AC catalyst. Appropriate amount of Fe improved metal dispersion and CO uptake, thus leading to the enhancement of catalytic activity. Moreover, the increased selectivity towards C 1 -C 16 alcohols was attributable to the formation of Co 2 C species and Co-Fe alloy promoted by moderate Fe loading in the 15Co/AC catalyst. The 15Co0.5Fe/AC catalyst showed the highest specific activity and yield of alcohols. In particular, the alcohols fraction in the liquid phase products improved up to 75% with the addition of Fe doping of 3 wt% on the 15Co/AC catalyst. It was suggested that Co/Co 2 C and Co-Fe alloy were responsible for the higher alcohols synthesis via CO hydrogenation over the15CoxFe/AC catalysts. [ABSTRACT FROM AUTHOR]

Abstract: Activated carbon-supported La-promoted Co catalysts with different La dopings (15Co–xLa/AC) were prepared by the co-impregnation method and investigated by means of CO hydrogenation, XRD, TPR-MS, CO adsorption and TPSR-MS techniques. The results showed that mixed linear α-alcohols (C1–C18) can be directly synthesized from syngas over the La-doped 15Co/AC catalysts under mild conditions and that the selectivity towards alcohols was improved by doping La into the 15Co/AC catalysts. It was found that the reducibility of the 15Co–xLa/AC catalyst decreased and the Co dispersion improved due to the strong interaction between Co and La2O3 species. La2O3 can promote the formation of cobalt carbides (Co2C), which are postulated to play an important role in the syntheses of the mixed linear α-alcohols. On the other hand, high Co dispersion and an appropriate ratio of Co2+/Co0 can enhance the activity of CO hydrogenation. [Copyright &y& Elsevier]

[Display omitted] • Supported ReCu catalysts were synthesized for DMO hydrogenation to ethanol. • The Re 2 Cu 5 /ZrO 2 catalyst exhibited the best catalytic performance. • The molar ratio of Cu0 and Cu+, reduction degree and copper particle size play the pivotal role. • Good stability of Re 2 Cu 5 /ZrO 2 catalyst. Addition of oxophilc rhenium to decorate small copper nanoparticles has been validated to be an efficient method to prepare a low-copper catalyst for the direct synthesis of ethanol via dimethyl oxalate (DMO) hydrogenation process, and herein we investigated the impact of supports on the catalytic performance of ReCu catalysts. A series of materials including activated carbon (AC), Al 2 O 3 , SiO 2 , TiO 2 and ZrO 2 were utilized as the support and as prepared Re 2 Cu 5 catalysts were evaluated. The results exhibited that the Re 2 Cu 5 /ZrO 2 catalyst possesses the highest DMO hydrogenation activity and ethanol yield (∼93%), which may be due to its lowest Cu0/Cu+ ratio (0.13), smallest Cu particle size (∼0.84 nm) a relative high reduction degree (59%). The CO adsorption behavior characterized by in si tu IR spectroscopy showed that a strong metal-support interaction creates an electron deficient environment of Cu nanoparticle, resulting in a lower Cu0/Cu+ ratio that enhances the activation of C O bond in the DMO molecular. [ABSTRACT FROM AUTHOR]

Promotional effects of oxygen vacancies of spinel catalysts in CO 2 hydrogenation are reported in early works, but the mechanistic origins remain elusive. Here, CoAl 2 O 4 spinels with varying numbers of oxygen vacancies are deliberately designed by a sol-gel method and different post-treatments. By combining catalytic testing, advanced electron microscopic and spectroscopic characterizations, and computational studies, the unusual oxygen vacancy-dependent catalytic behaviors are rationalized. Our work reveals that i) perfect spinel crystals possessing least oxygen vacancies can effectively constrain the Co2+ species at working conditions that are less active but selective to CO; and ii) vacancy-rich spinels promote both H 2 and CO 2 activations and COOH* formation, explaining the higher hydrogenation activity, but overwhelming vacancies cause Co2+ reduction and promote direct CO 2 * dissociation to CO* and deep hydrogenation to CH 4. These molecular-level understandings reinforce the idea of proper design of oxygen vacancies to achieve activity-selectivity balance. [Display omitted] • CoAl 2 O 4 spinels with different numbers of oxygen vacancies were designed. • CoAl 2 O 4 spinels presented divergent CO 2 hydrogenation performances. • Complex interplay among oxygen vacancies, catalyst structure and CO 2 hydrogenation performances were revealed. • Mechanistic origins of the multifaceted roles of oxygen vacancies were unveiled by DRIFT and DFT. [ABSTRACT FROM AUTHOR]

• Environmentally benign Cu-based catalysts are desirable for DMO hydrogenation. • Cu-Zn bimetallic catalysts with intimate metal contact are designed and tested. • Activity descriptor is reexamined and stability descriptor is unraveled. • High activity and excellent stability are achieved in the ethylene glycol production. The development of robust catalysts for selective hydrogenation of dimethyl oxalate (DMO) is key for the expansion of ethylene glycol (EG) production from C1 and renewable feedstocks. Copper-based catalysts promoted with Cr are industrially used, but it is desirable to develop more environmentally-benign alternatives. Silica-supported copper-zinc bimetallic catalysts featuring intimate metal contact are designed and used to establish the structure-performance relationships through combining in-depth characterizations with steady-state catalytic testing. Our study highlights: i) that the surface Cu0/Cu+ ratio is a reliable catalytic descriptor that determines the activity and selectivity, and ii) the importance of copper-zinc interface in stabilizing copper nanoparticles both under reduction and hydrogenation conditions. Controlled zinc doping allows fine tuning of these properties for the targeted reaction. Excellent performance has been achieved on the best-performing catalyst with >99.6% DMO conversion, >96.0% EG selectivity, and unprecedented stability of 800 h without catalyst deactivation, which represents a significant advance in the selective hydrogenations. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mo-doped Cu/SiO 2 catalysts were synthesized for DMO hydrogenation to ethanol. • The Mo 3 Cu 20 /SiO 2 sample exhibited the best ethanol yield (up to 94%). • The Lewis acidity and a balanced Cu0/Cu+ resulted from the interaction between MoO x and Cu NPs play the pivotal role. • Excellent stability of Mo 3 Cu 20 /SiO 2 catalyst. The environmentally-benign hydrogenation of dimethyl oxalate to produce ethanol has attracted considerable attention recently, and the yield of which remains a challenge for the commonly used Cu-based catalysts. Herein we reported a molybdenum-doped Cu catalyst synthesized by impregnating Mo on the Cu/SiO 2 composite prepared by an ammonia evaporation hydrothermal method, and the Mo 3 Cu 20 /SiO 2 sample exhibited the best compromise between activity and ethanol selectivity, acting as a robust catalyst (460 h time on stream) with a high ethanol yield (∼94 %). It is demonstrated that Mo doping elevates the amount of surface Cu+ species through the strong interaction between MoO x and Cu species, and the balanced Cu0/Cu+ ratio and enhanced surface acidity resulted by Mo addition afford the high ethanol selectivity through facilitating the dehydroxylation of ethylene glycol, whose activation energy over Mo 3 Cu 20 /SiO 2 is 79.9 kJ/mol, lower than that of Cu 20 /SiO 2 catalyst (108.1 kJ/mol). [ABSTRACT FROM AUTHOR]

The effect of iron promoter on the catalytic properties of Rh-Mn-Li/SiO2 catalyst in the synthesis of C2 oxygenates from syngas was investigated by means of the following techniques: CO hydrogenation reaction, temperature-programmed reduction (TPR), temperature-programmed desorption and reaction of adsorbed CO (CO-TPD and TPSR) and pulse adsorption of CO. The results showed that the addition of iron promoter could improve the activity of the catalysts. Unexpectedly, the yield of C2 oxygenates increased greatly from 331.6 up to 457.5 g/(kg h) when 0.05% Fe was added into Rh-Mn-Li/SiO2 catalyst, while no change in the selectivity to C2 oxygenates was observed. However, the activity and selectivity of C2 oxygenates were greatly decreased if the Fe amount exceeded 1.0%. The existence of a little iron decreased the reducibility of Rh precursor, while the reduction of Fe component itself became easier. CO uptake decreased with increasing the quantity of Fe addition. This phenomenon was further confirmed by CO-TPD results. The CO-TPD and TPSR results showed that only the strongly adsorbed CO could be hydrogenated, while the weakly adsorbed CO was desorbed. We propose that Fe is highly dispersed and in close contact with Rh and Mn; such arrangements were responsible for the high yield of C2 oxygenates. [Copyright &y& Elsevier]