Catalysis Letters

X-ray photoelectron spectroscopy measurements indicate that the Ce3+ fraction in Al2O3-supported CeO2 can be decreased by the incorporation of La3+. If La3+ is incorporated into the Al2O3 before CeO2 is added, a higher CeO2 dispersion and a greater range of reversible reducibility of the CeO2 may also be obtained. These changes offer potential for improvement in the oxygen storage capacity provided by CeO2 in three-way catalysts.

Chromium oxide supported on zirconia was prepared by dry impregnation of powdered Zr(OH)4with an aqueous solution of (NH4)2CrO4 followed by calcining in air. Upon the addition of only a small amount of chromium oxide (1 wt% Cr) to ZrO2, both the acidity and acid strength of the catalyst increased remarkably. The redox and catalytic behaviors of the samples were investigated through XPS and the reaction of cumene using a pulse technique. It was found that Cr6+ species existing on the surface of catalyst were responsible for the formation of strong acid sites and the catalytic activity for cracking of cumene. However, the Cr6+ species were easily reduced to Cr3+ species during the catalytic reaction of cumene and the reduced Cr3+ species were active for α-methylstyrene formation due to the dehydrogenation of cumene. The reduced Cr3+ species could be reoxidized by treatment with O2 and subsequently the reoxidized catalyst exhibited catalytic activity for the cracking reaction of cumene.

Pt, Pt–Sn and Pt–W supported on γ‐Al2O3 were prepared and characterized by H2 chemisorption, TEM, TPR, test reactions of n‐C8 reforming (500°C), cyclohexane dehydrogenation (315°C) and n‐C5 isomerization (500°C), and TPO of the used catalysts. Pt is completely reduced to Pt0, but only a small fraction of Sn and of W oxides are reduced to metal. The second element decreases the metallic properties of Pt (H2 chemisorption and dehydrogenation activity) but increases dehydrocyclization and stability. In spite of the large decrease in dehydrogenation activity of Pt in the bimetallics, the metallic function is not the controlling function of the bifunctional mechanisms of dehydrocyclization. Pt–Sn/Al2O3 is the best catalyst with the highest acid to metallic functions ratio (due to its lower metallic activity) presenting a xylenes distribution different from the other catalysts. The acid function of Pt–Sn/Al2O3 is tuned in order to increase isomerization and cyclization and to decrease cracking, as compared to Pt and Pt–W.

The concept of a hydrocarbon reformer trap is proposed as a novel technology for cleaning up automobile emissions. Zeolite beta with/without metal species such as iron, manganese, or cobalt is synthesized through a solid phase transformation of mesoporous (metallo)aluminosilicate MCM-41 along with tetraethylammonium cations for structure direction to zeolite beta. The microporosity of zeolite functions as a hydrocarbon trap, and the metal species inside the pores provide a reforming site.

A novel palladium-nanohybrid (Pd–Chitosan–CNT) catalytic composite has been developed using CNT–chitosan nanocomposite and palladium nitrate. The prepared catalytic platform displays excellent catalytic reactivity for the ipso-hydroxylation of various arylboronic acids with a mild oxidant aqueous H2O2 at room temperature, affording the corresponding phenols in excellent yields. Significantly, the easy recovery and reusability by simple manipulation demonstrate the green credentials of this catalytic platform.

A new polymer-anchored Cu(II) complex has been tested for the oxidation of sulfides and in oxidative bromination reaction with hydrogen peroxide as oxidant. Sulfides have been selectively oxidized to corresponding sulfoxides in excellent yields and in presence of KBr as bromine source, organic substrates have been selectively converted to mono bromo substituted compounds. The polymer-anchored Cu(II) catalyst could be easily recovered by simple filtration and reused more than six times without appreciable loss of its initial activity.

Cu/SiO2 catalyst prepared by the ammonia-evaporation (AE) method is the potential preferred catalyst for hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG). Although significant advancements have been obtained in the confirmation and influence factors of active species in the hydrogenation process, the relationship between the catalytic activity and the sensitive factors in the preparation or pretreatment process of the catalyst is still uncertain. In this paper, Cu/ZSM-5 catalysts for DMO hydrogenation to EG were prepared by the AE method using ZSM-5 molecular sieve with high silicon-alumina ratio (1500) as a support. The ZSM-5 support was pretreated by drying at 393 K for different hours and it was found that the surface hydroxyl group of the support had significant influence on the structure and catalytic hydrogenation performance of the prepared Cu/ZSM-5 catalyst. The distribution of surface hydroxyl groups could be significantly changed by pre-drying the carrier, which further resulted in the change of the copper dispersion and surface properties of subsequent copper-supported catalysts. With the decrease of hydroxyl content on the surface of the ZSM-5 support, the prepared reduced Cu/ZSM-5 catalyst possessed smaller Cu0 particles size, higher copper dispersion, higher surface area of Cu0 and Cu+ species, but weakened surface acidity of the catalyst, which resulted in the great improvement of the catalytic activity. The DMO conversion and EG selectivity could reach 100% and 93% even under the low reaction temperature at 448 K over the Cu/ZSM-5-24 catalyst (based on the ZSM-5 support pretreated by drying for 24 h). In addition, the catalytic activity did not show obvious change after 300 h of reaction, probably due to the low temperature reaction and suitable surface properties of the catalyst.

TiO2–graphene oxide (TiO2–GO) nanocomposites were prepared by the sol–gel method with different mass ratios of GO. The MnOX active components were loaded by means of ultrasonic impregnation. The catalysts exhibited excellent physical structures and electron transfer properties, which favored the catalytic activity. All of the catalysts were characterized by FESEM, XRD, TEM, BET, FT-IR, and XPS. The catalytic reduction activities of NOX were studied under low temperature conditions using ammonia as the reductant. Results indicated GO formation in the TiO2–GO supports, which reveals that TiO2–GO can be readily indexed as anatase TiO2 in all samples. Various valence states of manganese species coexisted in the MnOX/TiO2–GO catalysts. Non-stoichiometric (MnOX/Mn) on the surface of the composite catalysts was particularly beneficial to electron transfer, resulting in good redox performance. The optimum mass ratio of Mn in MnOX/TiO2–0.8 % GO was 9 wt%, and catalyst with this amount of Mn exhibited good resistance to H2O and SO2. All of the samples showed excellent N2 selectivity. The surface of the GO sheets is covered by a uniform layer of MnOX which increasing the activity of the catalyst by 9 % MnOX/TiO2–0.8 % GO.

Herein, a novel copper-catalyzed reaction of tosylmethylisocyanide (TosMIC) with benzyl alcohols has been developed using tert-butyl hydroperoxide (TBHP) for the first time. The reaction involves the in-situ oxidation of benzyl alcohol to corresponding benzaldehyde, followed by sequential formal [3+2] cycloaddition/radical addition/ring oxidation reactions, and provides an efficient method for the construction of 4-(tert-butylperoxy)-5-aryloxazol-2(3H)-ones from readily available starting materials. Replacement of TBHP with H2O2 led to the production of 5-aryloxazol-2(5H)-ones in good yields. Tandem oxidative Van Leusen reaction: efficient three-component approach for the synthesis of 4-(tert-butylperoxy)-5-aryloxazol-2(3H)-ones and 5-phenyloxazol-2(5H)-one for the first time.