The dry reforming of methane is a promising technology for the abatement of CH 4 and CO 2 . Ni−La 2 O 3 catalysts are characterized by their long-term stability (100 h) when tested at full conversion. The kinetics of dry reforming over these types of catalysts has been studied using both power-law and Langmuir− Hinshelwood-based approaches. However, these studies typically deal with fitting the net CH 4 rate, hence disregarding competing and parallel surface processes and the different possible configurations of the active surface. In this work, we synthesized a Ni−La 2 O 3 catalyst and tested six Langmuir−Hinshelwood mechanisms considering both single and dual active sites for assessing the kinetics of dry reforming and the competing reverse water−gas shift reaction and investigated the performance of the derived kinetic models. In doing this, it was found that: (1) all of the net rates were better fitted by a single-site model that considered that the first C−H bond cleavage in methane occurred over a metal−oxygen pair site; (2) this model predicted the existence of a nearly saturated nickel surface with chemisorbed oxygen adatoms derived from the CO 2 dissociation; (3) the CO 2 dissociation can either be an inhibitory or an irrelevant step, and it can also modify the apparent activation energy for CH 4 activation. These findings contribute to a better understanding of the dry reforming reaction's kinetics and provide a robust kinetic model for the design and scale-up of the process.
The accuracy
of the online quantification of gaseous effluents from catalytic reactors
by mass spectrometry (MS) is rarely addressed by researchers despite
the extensive use of the technique. MS results are strongly sensitive
to both the operation conditions of the reactor and to the state of
the instrument. Therefore, most studies use them as qualitative descriptors
of the performance of catalytic reaction systems. The purpose of this
work was to develop an accurate method for the quantification of gaseous
effluents from catalytic reactors. For this purpose, the mathematical
expressions from the so-called external and internal standard calibration
methods for MS were coupled to the typical metrics used for studying
catalytic reactions, namely, conversion, selectivity, and carbon mass
balances. The catalytic combustion of methane was selected as a model
reaction to test the developed approach. The accuracy of the developed
method was validated by comparison with results obtained in a separate
reaction system coupled online to a gas chromatograph. The closure
of the carbon mass balance was used as control metrics allowing for
the assessment of the physical meaning of the method. In general,
the internal standard method of calibration was found to be best for
the accurate quantification of gaseous streams by online mass spectrometry.
In general, the results of this investigation may be of use to researchers
in the field of catalysis as well as to research workers using mass
spectrometry for various purposes.
This work shows the compositional effect on low-temperature oxidation of crude oils subjected to in situ combustion (ISC). Three heavy crudes were used in this study in which detailed information on the molecular species involved in ISC was obtained by ultra-high-resolution mass spectrometry. The oxidation was carried out on a mixture of 2% of crude oil in Ottawa sand in an isothermal cell using a batch system at 1500 psi at three conditions: (i) reservoir temperature of each crude oil, (ii) 180 °C, and (iii) 180 °C using a heterogeneous catalyst-type β-MnO 2 . The oil remaining after the reaction was extracted from the sand and characterized by FT-ICR MS using (+) atmospheric pressure photoionization and (−) electrospray ionization modes. The acidity of the oxidation products (extracts) and the composition of the produced carbon oxides were also monitored. A greater amount of carbon oxides produced, a lower extraction yield of organic matter in the sand after the reaction, and a higher acidity in the extracts, implied a higher reactivity. In the same sense, a higher reactivity was observed for the sample with the highest sulfur content and over the most aromatic compounds. The use of the catalyst at 180 °C promoted the oxidative reactions in two of three of the oils, as well as the formation of polyoxygenated acids over monocarboxylic acids for one of the oils, which implies that the application of this technology strongly depends on the composition of the oil.
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