10 research outputs found
METHANE VALORIZATION OVER NOVEL CATALYST SYSTEMS VIA DIRECT PATHWAYS
Methane, when converted to higher hydrocarbons, promises a great future as the substituent for liquid petroleum in petrochemical and fine chemical industries. Methane conversion via direct pathways such as oxidative coupling of methane (OCM) to ethylene and direct non-oxidative methane conversion (DNMC) to C2 (acetylene, ethylene and ethane) and aromatics have attracted much attention given their unique capability in circumventing the intermediate energy-intensive steps found in indirect processes. In the OCM process, the more reactive nature of C2 products leads to the sequential oxidation of C2 to COx (CO or CO2). Selective catalysts that favor C2 formation are desired. The DNMC is challenged by low equilibrium conversion, high endothermicity, and high coke selectivity. Catalysts or reaction systems that concurrently solve these challenges are required.
This dissertation aims to develop novel catalyst systems to conquer limitations in OCM and DNMC to realize efficient and effective C2 production. For OCM reaction, hydroxyapatite (HAP), a bioceramic material with the capability of cation and/or anion substitutions, was innovatively employed as a catalyst. The effects of cation and/or anion substitutions in HAP on OCM reaction were studied. The rigorous description of the reaction kinetics of OCM in HAP-based catalysts was conducted. Finally, the selective control of exposed crystalline plane of HAP was realized to further understand the catalytic behaviors of HAP-based catalysts in OCM reactions. It is shown that cation and/or anion substitution can change the physicochemical properties of the HAP catalysts, and as consequences, the OCM catalytic performances. The c-surface (i.e., (002) crystalline plane) of HAP-based catalysts exhibited significant enhancement in areal rate in OCM reaction.
The single iron sites confined in the lattice of silica matrix (Fe/SiO2) is an emerging type of methane activation catalyst in DNMC. We innovated a millisecond catalytic wall reactor made of Fe/SiO2 catalyst to enabling stable and high methane conversion, C2+ selectivity, low coke yield, and long-term durability. These effects originate from initiation of DNMC by surface catalysis on reactor wall, and maintenance of the reaction by gas-phase chemistry in reactor compartment. Autothermal operation of the catalytic wall reactor is potentially feasible by coupling and periodical swapping of endothermic DNMC and exothermic oxidative coke removal on opposite side of the reactor. High carbon and thermal efficiencies and low cost in reactor materials are realized for the techno-economic process viability of the DNMC technology. In addition, we created a process of tailoring product selectivity towards to C2 hydrocarbons by employing a mixture of Fe/SiO2 catalyst and mixed ionic-electronic conductive perovskite (SrCe0.8Zr0.2O3âÎŽ) oxide in the presence of hydrogen co-feed in methane stream. The unprecedentedly high C2 yield was realized in DNMC reaction to maximize its potential as a feedstock for ethylene production in chemical industries
Understanding the Impact of Hydrogen Activation by SrCe 0.8Zr0.2O 3âÎŽ Perovskite Membrane Material on Direct Non-Oxidative Methane Conversion
Partial funding for Open Access provided by the UMD Libraries' Open Access Publishing Fund.Understanding the Impact of
Hydrogen Activation by
SrCe 0.8Zr0.2O 3âÎŽ Perovskite
Membrane Material on Direct
Non-Oxidative Methane Conversion
Sichao Cheng 1â , Su Cheun Oh 1â , Mann Sakbodin 1
, Limei Qiu 2
, Yuxia Diao 2 and Dongxia Liu 1
*
1 Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, MD, United States, 2 Research
Institute of Petroleum Processing, SINOPEC, Beijing, China
Direct non-oxidative methane conversion (DNMC) converts methane (CH 4 ) in one step to
olefin and aromatic hydrocarbons and hydrogen (H 2) co-product. Membrane reactors
comprising methane activation catalysts and H 2 -permeable membranes can enhance
methane conversion by in situ H 2 removal via Le Chatelierâs principle. Rigorous description
of H 2 kinetic effects on both membrane and catalyst materials in the membrane reactor,
however, has been rarely studied. In this work, we report the impact of hydrogen activation
by hydrogen-permeable SrCe 0.8Zr 0.2O 3âÎŽ (SCZO) perovskite oxide material on DNMC
over an iron/silica catalyst. The SCZO oxide has mixed ionic and electronic conductivity
and is capable of H2 activation into protons and electrons for H 2 permeation. In the fixed-
bed reactor packed with a mixture of SCZO oxide and iron/silica catalyst, stable and high
methane conversion and low coke selectivity in DNMC was achieved by co-feeding of H 2 in
methane stream. The characterizations show that SCZO activates H 2 to favor âsoft cokeâ
formation on the catalyst. The SCZO could absorb H 2 in situ to lower its local concentration
to mitigate the reverse reaction of DNMC in the tested conditions. The co-existence of H 2
co-feed, SCZO oxide, and DNMC catalyst in the present study mimics the conditions of
DNMC in the H2 -permeable SCZO membrane reactor. The findings in this work offer the
mechanistic understanding of and guidance for the design of H2 -permeable membrane
reactors for DNMC and other alkane dehydrogenation reactions.https://doi.org/10.3389/fchem.2021.80646
Effects of Controlled Crystalline Surface of Hydroxyapatite on Methane Oxidation Reactions
Hydroxyapatite
(HAP, Ca<sub>10</sub>(PO<sub>4</sub>)<sub>6</sub>(OH)<sub>2</sub>)
has a hexagonal prismatic structure that exposes
two crystalline surfaces: prism-faceted a- and basal-faceted c-surfaces.
In this work, the predominant exposure of c-surface was controlled,
and its influences in methane oxidation reactions (combustion and
oxidative coupling over HAP and lead-substituted HAP (Pb-HAP), respectively)
were studied. The c-surface exposure was realized by crystal orientation
in HAP-based catalyst film, which was created by an electrochemical
deposition of HAP seeds on a titanium substrate, followed by hydrothermal
crystallization and peeling off of the crystalline films from the
substrate. In comparison to a-surface that is prevalently exposed
in unoriented HAP-based catalysts, the c-surface (i.e., (002) crystalline
plane) of HAP-based catalysts exhibited up to 47-fold enhancement
in areal rate in both reactions. The distinct catalytic activity between
these two crystalline surfaces is attributed to the preferential formation
of oxide ions and vacancies on c-surfaces. The oxide ions and vacancies
in turns function as actives sites for promoting methane activation
and complete oxidation into CO<sub>2</sub>. Density functional theory
calculations confirmed the close relationship between different catalytic
activities in c-surface of oriented and a-surface of unoriented HAP
through the tendency of vacancy formation. Without the presence of
vacancies, the methyl or methylene group after methane activation
forms ethane or ethylene via coupling. The present study explored
the effects of HAP crystal orientation in methane oxidation reactions,
which revealed distinct catalytic behaviors of crystal surfaces in
HAP-based materials
Serial plasma and urine measurements of a patient with acute intoxication of zolpidem and flunitrazepam resulting in QT prolongation and ventricular tachycardia
Influence of humidity for preparing sol-gel ZnO layer: Characterization and optimization for optoelectronic device applications
Dual utilization of greenhouse gases to produce C2+ hydrocarbons and syngas in a hydrogen-permeable membrane reactor
Spatial distribution and catalytic performance of metalâacid sites in Mo/MFI catalysts with tunable meso-/microporous lamellar zeolite structures
Gold nanoparticles: preparation, properties, and applications in bionanotechnology
Gold nanoparticles (AuNPs) are important components for biomedical applications. AuNPs have been widely employed for diagnostics, and have seen increasing use in the area of therapeutics. In this mini-review, we present fabrication strategies for AuNPs and highlight a selection of recent applications of these materials in bionanotechnology