245 research outputs found
Reduction of stored NOx on a combined LNT-SCR reactor
No full textThe aim of the work is investigating the adsorption-reduction by H2 of NOx stored on a model LNT Pt-Ba/Al2O3 catalyst sample and on a combined LNT + Fe-ZSM5 SCR catalyst .
The storage of NOx over the LNT Pt-Ba/Al2O3 catalyst leads to nitrite formation at low temperatures, and to nitrate at high temperatures (above 300 °C). The stored NOx are reduced mainly to NH3 at low temperatures, and to N2 at high temperatures. In line with previous data and according to experiments carried out with H2 and NH3, a 2-step in series pathway for nitrogen formation is proposed involving at first the fast formation of ammonia upon reaction of NOx with H2, followed by the slower reaction of the so-formed ammonia with the stored NOx leading to N2. This 2-step in series pathway is able to account for the temporal evolution of the products which is observed during regeneration of LNT catalysts.
The presence of a Fe-ZSM5 SCR placed downstream the LNT catalyst is able to store NH3 released during the rich phase from the LNT sample. The stored ammonia is effectively converted to N2 during the subsequent lean phase, due to the occurrence of the SCR reaction over the Fe-ZSM5 catalyst layer. Hence the presence of a SCR catalyst layer placed downstream a LNT sample leads to the twofold benefit of reducing the NH3 slip and to increase the NOx removal efficiency. These advantages are very important at low temperatures, and tend to vanish at high temperatures where the NH3 slip is of less importance
Beyond Cultural Aphasia.
No full textA Conversation between Rossella Ciocca and the scholar and cultural activist G. N. Devy, author of the People's Linguistic Survey of India, about nomadic communities and their endangered languages and cultures
Author Spotlight: Rossella Palma
No full textDr. Rossella Palma ([email protected]) is a general surgeon who is currently a PhD student in the Section of
Experimental and Clinical Hepato-Gastroenterology at the
“Sapienza” University of Rome. She is primarily interested
in diagnostic and operative endoscopy for the treatment of
gastrointestinal diseases. She plans to pursue an academic
career following her PhD studies
NOx removal over a double-bed NSR-SCR reactor configuration
No full textA detailed analysis of the catalytic behaviour in the storage/reduction of NOx of single Pt–Ba/Al2O3 LNT
and FeZSM-5 SCR systems and of combined LNT + SCR configurations is analyzed and compared in this
work under clean conditions (i.e. in the absence of CO2 and H2O in the feed stream). By working under
dilute conditions (i.e. with low reductant concentrations) and with an inert purge between the lean and
the rich phases, nearly ideal isothermal conditions could be attained and the chemical pathways
operating in the each step of the NSR cycle could be analyzed for the investigated catalysts
configurations. It is found that when the SCR catalyst is placed downstream the NSR catalyst bed
(double-bed configuration), ammonia released from the LNT sample during the rich phase is stored on
the SCR catalyst placed downstreamand is then converted to N2 in the subsequent lean phase according
to the occurrence of a SCR reaction. This has a benefit on both the NOx removal efficiency and the N2
selectivity. If the zeolite SCR catalyst is mixed with the LNT sample (physical mixture), during the rich
phase the SCR catalyst traps ammonia which being intermediate in N2 formation leads to a decrease in
the evolution of nitrogen at the reactor outlet. Ammonia stored on the SCR catalyst then reacts with NOx
during the subsequent lean phase, leading to a significant N2 evolution: this increases the NOx removal
efficiency and the N2 selectivity if compared to the single Pt–Ba/Al2O3 catalyst sample
“Plurality, Identity, Democracy, Globalization…. A conversation with Sunil Khilnani” in Indiascapes. Images and words from globalized India
No full textRossella Ciocca interviews Sunil Khilnani author of the much appraised The Idea of India: one of the best non-fictional introductions to the complexities of politics in contemporary India. The strengths and weaknesses of present-day uneven modernity are discussed around a few strategic topics. First of all plurality, which in its linguistic, cultural, religious, ethnic variety has been vindicated since Independence as a foundational value, is seen as the quintessential resource for achosen practice of syncretism but also in danger of becoming the very source of fragmentation and implosion in a country increasingly maimed by fundamentalism and fanaticism. Democracy is then interrogated between the comfortable perspective of the firmly established and normally operating mechanisms of democratic routine, on the one hand, and the flawsof a still dramatically unjust system of distribution of rights and opportunities, on the other. Identity politics is in turn analysed both in its positive action of mobilizing society around the problem of social upgrading and in its unwelcome side effects of increasing practices of rigid and restricted classification fomenting division and violent sectarianism. In the end Indian growing cultural appeal upon the globalized scene is questioned in its complex relationship with the country’s quest for a role of protagonist in political as well as economic affairs upon a new multilateral international stage
The NOx reduction by CO on Pt-K/Al2O3 Lean NOx Trap Catalyst
No full textThe reduction by CO under dry conditions of NOx species stored at 350 °C onto a Pt−K/Al2O3 lean NOx trap catalyst is investigated by means of transient response methods (CO-TPSR and CO-ISC experiments) and complementary FT-IR spectroscopy. The results show that the pathway for the reduction of stored NOx by CO under dry and near isothermal conditions (and in the absence of CO2) is the same as that proposed by some of us in a previous work for a Pt−Ba/Al2O3 catalyst. In particular, (i) the reduction of stored NOx by CO occurs according to a Pt-catalyzed surface pathway that does not involve, as a first step, the release of NOx in the gas phase, is effective already at low temperature, and leads to nitrogen; (ii) the reaction scheme implies the formation of surface isocyanate species, followed by the reaction of these species with residual NOx to give nitrogen; and (iii) the reaction of NCO species with nitrates to give nitrogen is slightly slower than the reduction of nitrates to give NCO species; but on the Pt−K/Al2O3 catalyst, this last step is faster than on the Pt−Ba/Al2O3 system. As a consequence, the amount of isocyanate species present on the surface at the end of the reduction is lower for Pt−K/Al2O3 than for the Pt−Ba/Al2O3 catalyst
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