Borosilicate Molecular Sieve Research Articles

Boron removal and reinsertion studies in 10B–11B exchanged HAMS-1B (H-[B]-ZSM-5) borosilicate molecular sieves using solid-state NMR

Novel atomic-level insight in boron removal and reinsertion into the framework of a HAMS-1B (H-[B]-ZSM-5) borosilicate molecular sieve was obtained by a combination of wet chemistry and one-/two-dimensional 11B solid-state NMR (SSNMR) spectroscopy. Uncalcined HAMS-1B shows only tetrahedral boron. However, three boron species are observed in 11B SSNMR spectra of as-prepared and then calcined HAMS-1B: tetrahedral framework boron ([4]Bfr), trigonal framework boron ([3]Bfr), and non-framework trigonal boron ([3]BNF). A picture has emerged as to the origins of these three species. Trigonal boron species are formed via hydrolysis by reaction with the water formed from water release and water formed by oxidation and removal of the template during calcination. The trigonal boron species are readily removed from the framework by slurrying in water or mild acid solutions. Tetrahedral boron remains at a concentration about equal to that in the calcined sieve not slurried, indicating that it is more difficult to remove. The extent of boron removal and reinsertion is pH dependent. We demonstrate that boron is removed to a greater extent at low pH and can be reinserted when pH is increased. Boron reinsertion into the framework is proven by 11B SSNMR on a series of 10B–11B exchanged borosilicate zeolites. We found that when boron is reinserted it enters at higher concentrations (∼40% more) as tetrahedral boron, not trigonal boron, thus reversing partial hydrolysis and removal during calcination.

Gas-phase oxygen oxidation of alkylaromatics over CVD Fe/Mo/DBH: VIII. Alteration of the oxidation mechanism of xylenes by Ag-doping

The Ag-doped Fe/Mo/deboronated borosilicate molecular sieve, Ag/Fe/Mo/partially deboronated borosilicate molecular sieve (DBH), was prepared by impregnating an aqueous solution of AgNO 3 solution onto the calcined CVD Fe/Mo/DBH catalyst by the incipient wetness technique. The Ag-doped catalyst had surface area significantly lower than that of CVD Fe/Mo/DBH, and the Ag 2+ ions were enriched on the surface, and associated with Fe 2(MoO 4) 3 and MoO 3 phases. This brought about a dramatic change in the para-selective oxidation mechanism of xylenes exhibited by the undoped CVD Fe/Mo/DBH counterpart. Para-selective oxidation path as well as the side reactions were almost completely suppressed. The “pair” site responsible for the formation of terephthaldehyde in the p-xylene oxidation and acidic site of the DBH matrix causing the side reactions were almost completely poisoned by the Ag-doping. Consequently, p-tolualdehyde produced on the remaining “single” site became a predominant product at the expense of terephthaldehyde over Ag/Fe/Mo/DBH.

The CVD Fe/Mo/DBH (deboronated borosilicate molecular sieve)-catalyzed oxidation reactions

The CVD Fe/Mo/DBH (deboronated borosilicate molecular sieve) catalyst exhibits a para-selective property for the gas phase O 2 oxidations of a variety of alkylaromatic compounds. Novel reactions studied with the catalyst include selective synthesis of aldehydes, activation and utilization of CO 2 in the oxidation reactions, syntheses of oxygenates from alkenylaromatics, oxidative dehydrogenation reactions of alkylaromatics and alkanes. Terephthaldehyde, benzaldehyde and their derivatives are prepared from methylbenzenes, alkylaromatics, alkenylaromatics, and para-substituted toluene derivatives. Alkenylaromatics and olefins are formed from alkylaromatics and alkanes, respectively, as an initial dehydrogenated product. These reactions are described using the representative substrate(s) as an example, and the results are interpreted based on the para-selectivity based on the effects of various para-oriented substituents such as alkyl, alkenyl, hydroxy, methoxy and halide group. These reactions share a reaction mechanism involving the rate-determining hydrogen abstraction initiated by a common active species, ferric molybdate.

Reforming with Novel Borosilicate Molecular Sieve Catalysts

In recent years the cost of research is increasingly dear to the sponsoring organizations, whether we speak of the public or private sector. Yet to meet the demand to make advances in product-generating technologies and to do so with slimmer margins, cost savings have to be developed along the chain of process events needed for production. In addition, the public atlarge has voiced their mandate for more environmentally benign operations. One look at the program for the 5th World Congress of Chemical Engineering (San Diego, 1996) would quickly show this trend. Both of the above-mentioned concerns merge together in the world of the chemical producer, generating a call for breakthroughs in the synergy of combining advanced catalytic materials with novel engineering processes. Thus, catalysis remains a focal point for technological progress [1].Zeolites continue to be used as advanced catalytic materials, their contribution of molecular size discrimination, potential stability and high activity highlighting them as candidates for use in developing new process chemistry. Production of alkyl aromatics has seen recent trends in the replacement of existing corrosive catalyst technology by the safer solid acid zeolite catalysts [2]. The lube oil business has experienced the introduction of new Isodewaxing catalysts, capable of producing higher yields of desired product, and thereby reducing waste loss in the overall process scheme [3].

Gas-phase oxygen oxidations of alkylaromatics over CVD Fe/Mo/borosilicate molecular sieve. V. Para-selective oxidations of methylaromatics

Gas-phase oxygen oxidation of methylaromatics was studied over the chemical vapor deposited (CVD) M/Mo/partially deboronated borosilicate molecular sieve (DBH) catalysts (M = Fe, Sb, Zn, Bi, Zr or Sn). The methylaromatics include toluene, xylenes, pseudocumene, mesitylene and durene. These catalysts exhibited a unique property of catalyzing oxidation of the two para-oriented methyl substituents in polymethylated benzenes to form terephthaldehyde derivatives. The para-oriented methyl substituents play a key role in defining the catalytic activity and selectivity toward aldehyde. Terephthaldehyde and monoaldehyde derivatives were formed from p-xylene, pseudocumene, and durene while toluene was converted to benzaldehyde. m-Xylene and mesitylene remained unreactive over these catalysts.

Gas-phase oxygen oxidations of alkylaromatics over chemical vapor deposited Fe/Mo/borosilicate molecular sieve, Fe/Mo/DBH.: IV. Effect of supporting matrix on p-xylene oxidation

The CVD Fe/Mo/supporting matrix (borosilicate molecular sieve, ZSM-5 or silicalite) was studied for gas-phase oxygen oxidation of p-xylene. The partially deboronated borosilicate molecular sieve matrix (DBH) played a unique role for the selective aldehyde synthesis. Terephthaldehyde was produced over CVD Fe/Mo/DBH, while disproportionation of p-xylene became predominant over CVD Fe/Mo/ZSM-5. The CVD Fe/Mo/silicalite exhibited relatively low activity and poor aldehyde selectivity.

One-step hydroxylation of benzene to phenol. II. Gas phase N2O oxidation over Mo/Fe/borosilicate molecular sieve

The Fe/Mo/partially deboronated borosilicate molecular sieve catalyst prepared by the chemical vapor deposition (CVD) method was active for the selective formation of phenol by gas-phase N2O oxidation of benzene. The impregnated counterpart exhibited lower activity than the CVD catalyst. The borosilicate molecular sieve itself also was active. Two mechanistic paths are postulated based on reactive oxygen species such as O−, which can be generated via interaction of N2O with the iron sites in the CVD-borosilicate molecular sieve catalyst, or OH+, which can be generated by Bronsted sites on the borosilicate molecular sieve itself.

Gas-phase oxygen oxidations of alkylaromatics over chemical vapor deposited Fe/Mo/borosilicate molecularsieve, Fe/Mo/DBH: I. The selective synthesis of terephthaldehyde from para-xylene

The Fe/Mo/borosilicate molecular sieve catalyst, Fe/Mo/DBH (Mo/Fe = 1.6–2.0), was prepared from FeCl 3, MoO 2Cl 2 and partially deboronated borosilicate molecular sieve (DBH) by the chemical vapor deposition method. The Fe/Mo/DBH catalyst exhibited a stable para-selective oxidation activity to form terephthaldehyde with high selectivity by the gas-phase oxygen oxidation of para-xylene under mild reaction conditions. para-Tolualdehyde was also formed in the reaction, and a molar ratio of terephthaldehyde to para-tolualdehyde in the product was ca. 2–4 to 1. Despite the large surface area of the catalyst, 250–325 m 2/g, substrate burning was suppressed to less than 10% under controlled conditions. A mechanism featuring two different types of active sites, the “pair” sites for terephthaldehyde and “single” sites for para-tolualdehyde, is postulated.