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Natural gas at remote locations would greatly benefit from on-site processing using modular technologies such as dehydroaromatization (DHA). This work models an intensified DHA process to increase product yield and methane conversion by coupling the reactor with a chemical looping unit that effectively separates hydrogen through a redox cycle and a temperature swing adsorption process to remove the aromatics and water and recycle unconverted methane. We postulate dynamic models and steady-state surrogate models to analyze and optimize the production of the aromatic product. The optimum methane conversion of 48% and the aromatic yield of 42% occur at a recycle ratio of 0.47 and a reactor temperature of 725 degrees C. 

We report that boron -containing zeolite chabazite (B-CHA) catalyzes the oxidative dehydrogenation of ethane (ODHE) with high selectivity (>70 %) and excellent stability in the temperature range of 500-600 degrees C. ODHE rates, in fact, increase over time on stream. Ethane consumption rate has an apparent activation energy of 126 kJ mol(-1), with Langmuirian dependence on the oxygen partial pressure and first-order dependence on the ethane partial pressure. Investigation of the catalyst before and after reaction by one-dimensional B-11 magic angle spinning (1D B-11 MAS) nuclear magnetic resonance (NMR), two-dimensional B-11 multiple quantum MAS (2D B-11 MQMAS) NMR spectroscopy, and Fourier transform infrared (FTIR) spectroscopy identifies the B-OH group in defect trigonal boron (B(OSi)(OH)(2)) as the species initiating the ODHE reaction. This result could open a pathway to develop suitable catalysts for industrial ethylene production with lower greenhouse gas emissions than current non -oxidative dehydrogenation routes. 

The effect of olefin addition to a stream of dimethyl ether on the methanol homologation reaction is investigated using iron-substituted zeolites Fe-beta and Fe-ZSM-5. The reaction was investigated using plug-flow microreactors in the temperature range of 240-400 degrees C, at a total pressure of 0.239 MPa and a WHSV of 6.12 (g DME/ gcat-hr). For Fe-beta (Si/Fe= 9.2) catalysts, isobutene co-feeding almost doubles dimethyl ether (DME) consumption rate and shifts selectivity towards larger olefins with carbon numbers from 5 to 7. Addition of isobutene above 6.3%, however, resulted in a reduction of DME consumption rates, an effect assigned to the replacement of surface methoxy groups for adsorbed olefins in the zeolite pores. Below a temperature of 340 degrees C hydride-transfer rates are negligible; reaction rates are stable for over 5.5 h and the products consist almost exclusively of olefins and a small amount of methane. Above 360 degrees C the onset of catalytic hydride transfer processes is observed leading to fast catalyst deactivation rates and an increase in the concentration of aromatic species. Iron ZSM-5 (Si/Fe = 21.4) catalysts under similar reaction conditions consumes methanol faster than Febeta at approximately three times the TOF (on a per iron basis). The Fe-ZSM-5 catalyst was selective to a distribution of products (C5 to C8) as compared to Fe-beta which was selective to primarily C5 and C7. Co-feeding larger olefins (2-methyl-2-butene, 2,3-dimethyl-2-butene, 2,3,3-trimethyl-1-butene, and 2,4,4-trimethyl-2-pentene) at a 3.9% olefin concentration over Fe-beta changed selectivity towards cracking products (C4 compounds such as isobutene). As the size of the olefin increases, a reduction of DME consumption rate is also observed. These results show that co-feeding olefins with DME over Fe-zeolites is a promising route to increase methylation rates at relatively low temperatures producing larger branched olefins and that the product distribution is highly dependent on the zeolite pore size and structure of the olefin. 

Ga-and In-exchanged chabazite (CHA) zeolites with same Si/Al and metal/Al ratios were prepared via the incipient wetness impregnation method, were characterized using N-2 adsorption, electron microscopy, temperature-programed reactions and were evaluated for the ethane dehydrogenation reaction using flow microreactors. Ga-CHA has higher reaction rates and a lower activation energy of 107 kJ/mol than In-CHA (E-a = 175 kJ/mol). Rietveld refinement of the X-ray powder diffraction pattern shows that the In+ cation is predominantly located above the 6-ring of the CHA cage. It is proposed that the reaction proceeds through the alkyl mechanism based on stability of alkyl hydride intermediates as determined using DFT calculations. The oxidative addition of ethane to the metal shows much lower Gibbs free energy for Ga-CHA (+27.95 kJ/mol) vs In-CHA (+124.85 kJ/mol). These results indicate that oxidative addition may be the rate-limiting step of ethane dehydrogenation in these materials. 

Indium on silica, alumina and zeolite chabazite (CHA), with a range of In/Al ratios and Si/Al ratios, have been investigated to understand the effect of the support on indium speciation and its corresponding influence on propane dehydrogenation (PDH). It is found that In 2 O 3 is formed on the external surface of the zeolite crystal after the addition of In(NO 3 ) 3 to H-CHA by incipient wetness impregnation and calcination. Upon reduction in H 2 gas (550 °C), indium displaces the proton in Brønsted acid sites (BASs), forming extra-framework In + species (In-CHA). A stoichiometric ratio of 1.5 of formed H 2 O to consumed H 2 during H 2 pulsed reduction experiments confirms the indium oxidation state of +1. The reduced indium is different from the indium species observed on samples of 10In/SiO 2 , 10In/Al 2 O 3 ( i.e. , 10 wt% indium) and bulk In 2 O 3 , in which In 2 O 3 was reduced to In(0), as determined from the X-ray diffraction patterns of the product, H 2 temperature-programmed reduction (H 2 -TPR) profiles, pulse reactor investigations and in situ transmission FTIR spectroscopy. The BASs in H-CHA facilitate the formation and stabilization of In + cations in extra-framework positions, and prevent the deep reduction of In 2 O 3 to In(0). In + cations in the CHA zeolite can be oxidized with O 2 to form indium oxide species and can be reduced again with H 2 quantitatively. At comparable conversion, In-CHA shows better stability and C 3 H 6 selectivity (∼85%) than In 2 O 3 , 10In/SiO 2 and 10In/Al 2 O 3 , consistent with a low C 3 H 8 dehydrogenation activation energy (94.3 kJ mol −1 ) and high C 3 H 8 cracking activation energy (206 kJ mol −1 ) in the In-CHA catalyst. A high Si/Al ratio in CHA seems beneficial for PDH by decreasing the fraction of CHA cages containing multiple In + cations. Other small-pore zeolite-stabilized metal cation sites could form highly stable and selective catalysts for this and facilitate other alkane dehydrogenation reactions.