A simplified route to the synthesis of CMK-3 replica based on precipitation polycondensation of furfuryl alcohol in SBA-15 pore system

A novel method of synthesis of mesoporous, polymer-derived CMK-3 carbon replica was proposed. Instead of a multi-stage, time-consuming and toxic solvent involving procedure, the direct, acid-catalyzed precipitation polycondensation of furfuryl alcohol to poly(furfuryl alcohol) (PFA), as the carbon precursor, in the pore system of SBA-15 silica was used. The optimal PFA/SBA-15 mass ratio resulting in the complete pore filling was found. The final carbon material was obtained by carbonization of the formed composite and subsequent removal of silica by treatment with HF. Low-temperature sorption of nitrogen, powder X-ray diffraction and transmission electron microscopy confirmed the formation of well-ordered, hexagonal carbon mesostructure. The produced CMK-3 exhibited the presence of oxygen-containing surface groups, recognized as mainly carbonyl and carboxyl species by X-ray photoelectron spectroscopy and temperature-programmed desorption. The presence ofthese groups caused the mesoporous carbon to be catalytically active in the oxidative dehydrogenation of ethylbenzene to styrene.This work was supported by the National Science Centre under the Grant No. DEC–2011/01/N/ST5/05595. Rafał Janus wishes to thank the Foundation for Polish Science MPD Programme co-financed by the EU European Regional Development Fund for the financial support. The research was carried out with the equipment purchased thanks to the financial support of the European Regional Development Fund in the framework of the Polish Innovation Economy Operational Program (contract No. POIG.02.01.00-12-023/08)

Chemically activated poly(furfuryl alcohol)-derived CMK-3 carbon catalysts for the oxidative dehydrogenation of ethylbenzene

The surface of CMK-3 carbon, synthesized by the reversible replication of mesoporous silica (SBA-15) using poly(furfuryl alcohol) as a carbon precursor, was activated by wet oxidation with an aqueous solution of HNO3 or H2O2. The process was performed at 50 °C using solution containing different concentrations of the oxidizing agent. It was found that during the modification no significant changes in textural and structural properties of CMK-3 replica occurred. However, the treatment resulted in the formation of appreciable amounts of surface species containing oxygen. XPS and DRIFT spectroscopy allowed to identify and quantify the surface functional groups. Their stability was studied by TG-FTIR measurements. CO and CO2 were found as main gaseous products evolved during thermal decomposition under inert atmosphere. Finally, the modified samples were tested in the catalytic oxidative dehydrogenation of ethylbenzene to styrene at 350 °C in the presence of oxygen as an oxidizing agent (at O2/ethylbenzene molar ratio of 1.0 and 3.0). At the beginning of the catalytic run, the highest styrene yield and selectivity was achieved at the lower O2 content over the catalysts treated with nitric acid. Nevertheless, all studied catalysts underwent a gradual deactivation due to coke formation and changes in the distribution of surface moieties.This work was supported by the Polish National Science Centre under the grant no. DEC–2011/01/N/ST5/05595. The research was carried out with the equipment purchased thanks to the financial support of the European Regional Development Fund in the framework of the Polish Innovation Economy Operational Program(contract No. POIG.02.01.00-12-023/08)

Catalytic behavior of chromium oxide supported on nanocasting-prepared mesoporous alumina in dehydrogenation of propane

Mesoporous alumina with narrow pore size distribution centered in the range of 4.4–5.0 nm and with a specific surface area as high as 270 m2·g−1 was prepared via the nanocasting approach using a CMK-3 carbon replica as a hard template. Based on this support, a series of catalysts containing 1, 5, 10, 20 and 30 wt % of chromium was prepared by incipient wetness impregnation, characterized, and studied in the dehydrogenation of propane to propene (PDH). Cr species in three oxidation states—Cr(III), Cr(V) and Cr(VI)—were found on the oxidized surface of the catalysts. The concentration of these species varied with the total Cr loading. Temperature-programmed reduction (H2-TPR) and UV-Vis diffuse reflectance spectroscopy (UV-Vis-DRS) studies revealed that Cr(VI) species dominated at the lowest Cr content. An increase in the Cr loading resulted in an appearance of an increasing amount of Cr(III) oxide. UV-Vis-DRS measurements performed in situ during the PDH process showed that at the beginning of the catalytic test Cr(VI) species were reduced to Cr(III) redox species. A crucial role of the redox species in the PDH process over the catalysts with the low Cr content was confirmed. The stability test for the catalyst containing 20 wt % of Cr showed that this sample exhibited the reproducible catalytic performance after the first four regeneration–dehydrogenation cycles. Moreover, this catalyst had higher resistance on deactivation during the PDH process as compared to the reference catalyst with the same Cr loading, but was supported on commercially available alumina

Oxidative Dehydrogenation of Ethylbenzene Over Poly(furfuryl alcohol)-Derived CMK-1 Carbon Replica

Poly(furfuryl alcohol) was introduced into a pore system of MCM-48 silica by the precipitation polycondensation of furfuryl alcohol (FA). The complete filling of the pores without the deposition of significant amounts of polymer on the external surface of MCM-48 was obtained at the FA/MCM-48 mass ratio close to 1.0. The final structure of carbon replica was formed by subsequent carbonization and extraction of SiO2 with HF. The carbonization temperature strongly influenced the surface composition of the formed carbon replicas. The highest catalytic activity in the oxidative dehydrogenation of ethylbenzene was observed for CMK-1 with the highest concentration of phenol and carbonyl groups, recognized as active sites of the studied reaction.This work was supported by the National Science Centre under the Grant No. 2013/09/B/ST5/03419. The research was carried out with the equipment purchased thanks to the financial support of the European Regional Development Fund in the framework of the Polish Innovation Economy Operational Program (contract No. POIG.02.01.00-12-023/08)

Chemical activation of mesoporous carbon replicas resulting in formation of surface oxygen-containing sites

W niniejszej pracy przeprowadzono optymalizację nowej metody syntezy repliki węglowej typu CMK-3. W pierwszym jej etapie otrzymano twardy templat krzemionkowy typu SBA-15, którego pory wypełniono następnie prekursorem węglowym stosując reakcję polikondensacji strąceniowej alkoholu furfurylowego w środowisku wodnym. Uzyskany kompozyt polimerowo-krzemionkowy poddano karbonizacji w celu przekształcenia części organicznej w postać czysto węglową. Ostatnim etapem syntezy było wymycie templatu za pomocą kwasu fluorowodorowego. Przygotowano materiały oparte na różnych stosunkach masowych poli(alkoholu furfurylowego) do SBA-15. Uzyskane preparaty scharakteryzowano przy użyciu metod BET, XRD, TG, XPS oraz TEM, a następnie przebadano w roli katalizatorów w reakcji utleniającego odwodornienia etylobenzenu do styrenu stosując różne ilości czynnika utleniającego. Zebrane wyniki pokazały, że tlen obecny w środowisku reakcyjnym aktywuje powierzchnię węgla tworząc grupy karbonylowe i hydroksylowe uważane za centra aktywne procesu. Optymalne właściwości wykazywała próbka otrzymana na bazie preparatu o zakładanym stosunku masowym PFA/SBA-15 równym 2,00. Odpowiednim stężeniem czynnika utleniającego okazał się stosunek O2:etylobenzen równy 9:1, dla którego zarejestrowano największą wartość stopnia konwersji etylobenzenu przy wysokiej wydajności styrenu.In the presented work a novel method of the synthesis of CMK-3 type carbon replica was optimized. In the first step, hard silica template, namely SBA-15, was obtained. The pore system of mesoporous silica was filled out by a carbon precursor using precipitation polycondensation of poly(furfuryl alcohol) in water. After carbonization of the obtained polymer-silica composite, the hard template was removed by dissolving in hydrofluoric acid solution. The carbon replicas based on various mass ratio between poly(furfuryl alcohol) and SBA-15 were synthesized. The prepared materials were characterized by different methods (BET, XRD, TG, XPS and TEM) and subsequently tested in a role of catalysts in the process of oxidative dehydrogenation of ethylbenzene to styrene using various contents of oxidizing agent in the feed. The collected results showed that oxygen present in the reaction system activates the surface of carbon catalyst promoting the formation of oxygen-containing functional groups (carbonyl and hydroxyl) considered to be real active sites. The optimal catalytic performance was achieved for the carbon replica synthesized using the mass ratio of PFA/SBA-15 = 2.00. The highest conversion of ethylbenzene and yield of styrene was observed over this catalyst at the molar ratio of O2/ethylbenzene of 9:1

Mesoporous carbon materials as promising catalysts for oxidative dehydrogenation of alkanes

Atrakcyjne właściwości, do których zaliczyć można rozwiniętą powierzchnię właściwą, uporządkowany układ szerokich kanałów wewnątrz ziarnowych oraz obecność względnie dużej liczby powierzchniowych grup tlenowych, sprawiają, że mezoporowate materiały węglowe cieszą się ogromnym zainteresowaniem licznych grup badawczych związanych z chemią materiałów oraz katalizą. W pracy przedstawiono krótki przegląd dotyczący możliwości użycia materiałów węglowych o kontrolowanej mezostrukturze jako katalizatorów reakcji utleniającego odwodornienia alkanów.Peculiar properties, such as a high specific surface area, an ordered arrangement of wide intraparticle pores as well as a relatively high concentration of surface oxygen-containing functional groups, make mesoporous carbons interesting materials for various research groups working in the field of materials chemistry and catalysis. In this work, a short review concerning the possibility of application of carbon materials with controlled mesostructure as catalysts for the oxidative dehydrogenation of alkanes is presented