Incidence of orthostatic hypotension and cardiovascular response to postoperative early mobilization in patients undergoing cardiothoracic and abdominal surgery

Background: In cardiothoracic and abdominal surgery, postoperative complications remain major clinical problems. Early mobilization has been widely practiced and is an important component in preventing complications, including orthostatic hypotension (OH) during postoperative management. We investigated cardiovascular response during early mobilization and the incidence of OH after cardiothoracic and abdominal surgery. Methods: In this prospective observational study, we consecutively analyzed data from 495 patients who underwent elective cardiothoracic and abdominal surgery. We examined the incidence of OH, and the independent risk factors associated with OH during early mobilization after major surgery. Multivariate logistic regression was performed using various characteristics of patients to identify OH-related independent factors. Results: OH was observed in 191 (39%) of 495 patients. The incidence of OH in cardiac, thoracic, and abdominal groups was 39 (33%) of 119, 95 (46%) of 208, and 57 (34%) of 168 patients, respectively. Male sex (OR 1.538; p = 0.03) and epidural anesthesia (OR 2.906; p < 0.001) were independently associated with OH on multivariate analysis. Conclusions: These results demonstrate that approximately 40% patients experience OH during early mobilization aftercardiothoracic and abdominal surgery. Sex was identified as an independent factor for OH during early mobilization after all three types of surgeries, while epidural anesthesia was only identified after thoracic surgery. Therefore, the frequent occurrence of OH during postoperative early mobilization should be recognized

Catalyst systems for selective catalytic reduction + NO: X trapping: From fundamental understanding of the standard SCR reaction to practical applications for lean exhaust after-treatment

We have developed chemical trapping techniques as a novel tool to assess the nature of unstable reaction intermediates in the standard SCR reaction at low temperatures (120-200 °C). For this purpose, we have conducted transient response experiments over mechanical mixtures of an SCR catalyst (Fe-ZSM-5 or Cu-CHA) and a NOx storage material (BaO/Al2O3), which is able to trap and stabilize highly reactive NOx species. The results conclusively confirm that NO oxidative activation forms a gaseous intermediate, which acts like a nitrite precursor (e.g. HONO/N2O3) and is eventually stored on BaO/Al2O3. Such a species is also able to react with ammonia to produce N2, and is therefore proposed as a key intermediate of the standard SCR mechanism. We have further demonstrated that the capability of chemical trapping mechanical mixtures to capture NO in O2 at low temperature can also be exploited in practical applications for NOx emission control during cold start transients of diesel vehicles. In fact, such systems (SCR catalyst + NOx storage material) are characterized by an intrinsic dual functionality, being able both to store NOx when urea cannot be injected (e.g. below 170 °C) and to reduce the stored NOx with ammonia at higher temperatures in a single device. Accordingly, these mixtures have been renamed adsorption + selective catalytic reduction (AdSCR) systems. This review will summarize the main results achieved when implementing mechanical mixtures of NOx adsorbers and SCR catalysts both for fundamental understanding of the standard SCR mechanism and for abatement of cold start emissions

AdSCR Systems (Adsorption + Selective Catalytic Reduction): Analysis of the Influence of H2O and CO2 on Low Temperature NOx Emission Reduction Performances

The removal of NOx from low-temperature diesel engine emissions still represents a big challenge in view of the upcoming more stringent worldwide regulations. In our previous studies, we proved the ability of novel AdSCR (Adsorption + Selective Catalytic Reduction) systems, based on the combination of a chemical trapping compound and a conventional SCR catalyst, to trap cold start NOx emissions and to desorb and simultaneously reduce them with ammonia at higher temperature. In the present work, we extend the investigation of Cu-CHA + BaO/Al2O3 systems under more realistic conditions, focusing on the impact of H2O and CO2. The experimental results reveal a reduction of the AdSCR system performances with respect to dry and CO2-free conditions. Despite this, the system is still able to store and reduce NOx. The NOx storage capacity on barium oxide is more affected by the presence of CO2 than by H2O. However, H2O hinders the NO oxidative activation in the zeolite cages, which is a fundamental step in order to be able to trap NOx on the storage material at low temperature. We further demonstrate that the detrimental effect of H2O can be mitigated by small amounts of NO2 in the gaseous feed or by including a 13X zeolite guard bed prior to the AdSCR bed

Unraveling the Hydrolysis of Z2Cu2+to ZCu2+(OH)-and Its Consequences for the Low-Temperature Selective Catalytic Reduction of NO on Cu-CHA Catalysts

As the state-of-the-art catalyst for the selective catalytic reduction (SCR) of NOx, Cu-CHA has been extensively investigated in both its practical and fundamental aspects. Among the latter, how Z2Cu2+, an active site for SCR, participates in low-temperature (LT) SCR reactions remains debated. Here, we propose a scheme involving the hydrolysis of Z2Cu2+ to ZCu2+(OH)-, a thermodynamically and kinetically favorable process under LT-SCR conditions, based on multiple pieces of evidence from a probe reaction (transient CO oxidation), transient Cu2+ reduction kinetic runs, in situ FTIR spectroscopy, and first-principles calculations. Such an integrated investigation reveals unambiguously that the hydrolysis of Z2Cu2+ to ZCu2+(OH)- occurs facilely in the presence of NH3, which may thus reconcile the identical quadratic kinetics of Z2Cu2+/ZCu2+(OH)- reduction with the inactivity of Z2Cu2+ in the formation of Cu2+ pairs. Accordingly, we highlight that NH3-assisted hydrolysis plays a critical role in LT-SCR and should be taken into account especially when discussing SCR reaction details over Z2Cu2+

The h2o effect on cu speciation in cu-cha-catalysts for nh3-scr probed by nh3 titration

The present work is focused on the effect of water on NH3 adsorption over Cu-CHA SCR catalysts. For this purpose, samples characterized by different SAR (SiO2/Al2O3 ) ratios and Cu loadings were studied under both dry and wet conditions. H2O adversely affects NH3 adsorption on Lewis acid sites (Cu ions) over all the tested catalysts, as indicated by the decreased NH3 desorption at low temperature during TPD. Interestingly, the NH3/Cu ratio, herein regarded as an index for the speciation of Cu cations, fell in the range of 3–4 (in the presence of gaseous NH3 ) or 1–2 (no gaseous NH3 ) in dry conditions, in line with the formation of different NH3-solvated Cu species (e.g., [CuII (NH3 )4 ]2+ and [CuII (OH)(NH3 )3 ]+ with gaseous NH3, [Z2CuII (NH3 )2 ]2+ and [ZCuII (OH)(NH3 )]+ without gaseous NH3 ). When H2O was fed to the system, on the contrary, the NH3/Cu ratio was always close to 3 (or 1), while the Brønsted acidity was slightly increased. These results are consistent both with competition between H2O and NH3 for adsorption on Lewis sites and with the hydrolysis of a fraction of Z2CuII species into ZCuIIOH

Analysis of AdSCR Systems for NOx Removal During the Cold-Start Period of Diesel Engines

Herein, we extend the study of the AdSCR system (AdSCR = adsorption + selective catalytic reduction), consisting in a physical mixture of a conventional NH3-SCR catalyst and of a NOx storage material. We have shown in previous work that an AdSCR system can capture and store NOx at room temperature from Diesel engine exhausts, and directly reduce them with ammonia at higher temperatures in the same unit. The present work aims at optimizing the system composition, in order to minimize the release of NOx in the low temperature window. Results from cold start mimicking experiments show that the full storage time, i.e. the zero-emission period where the fed NO is completely adsorbed by the catalyst, is affected only by the amount and the composition of the storage material, whereas the NOx storage efficiency is controlled by amount and nature of both components of the physical mixture

Unexpected Low-Temperature deNOx Activity of AdSCR Systems for Cold Start NOx Abatement

Low-temperature operation of urea selective catalytic reduction (SCR) aftertreatment systems for the abatement of NOx from diesel engines presents new challenges related to poor catalytic activity and the urea injection temperature threshold. Physical mixtures of a NH3-SCR catalyst (e.g., Fe-/Cu-zeolite) and of a NOx storage material (e.g., BaO/Al2O3, CeO2/Al2O3) have shown promising performances in terms of overall NOx removal efficiency, as they can operate both as NOx adsorbers, trapping NOx during the cold start transient, and as SCR catalysts, reducing at higher temperatures the previously stored NOx with NH3. Herein, we extend the investigation of new Cu-CHA + BaO/Al2O3 AdSCR systems (AdSCR = adsorption + selective catalytic reduction) focusing on the reactivity between NOx and ammonia in the low-temperature window (from room temperature up to 170&nbsp;°C). We find that the selective reduction of NO by NH3 over Cu-CHA is surprisingly enhanced by the presence of BaO/Al2O3 when ammonia is preadsorbed, leading to the onset of nitrogen formation already at 40&nbsp;°C

On the Redox Mechanism of Low-Temperature NH3-SCR over Cu-CHA: A Combined Experimental and Theoretical Study of the Reduction Half Cycle

Cu-CHA is the state-of-the-art catalyst for the Selective Catalytic Reduction (SCR) of NOx in vehicle applications. Although extensively studied, diverse mechanistic proposals still stand in terms of the nature of active Cu-ions and reaction pathways in SCR working conditions. Herein we address the redox mechanism underlying Low-Temperature (LT) SCR on Cu-CHA by an integration of chemical-trapping techniques, transient-response methods, operando UV/Vis-NIR spectroscopy with modelling tools based on transient kinetic analysis and density functional theory calculations. We show that the rates of the Reduction Half-Cycle (RHC) of LT-SCR display a quadratic dependence on CuII, thus questioning mechanisms based on isolated CuII-ions. We propose, instead, a CuII-pair mediated LT-RHC pathway, in which NO oxidative activation to mobile nitrite-precursor intermediates accounts for CuII reduction. These results highlight the role of dinuclear Cu complexes not only in the oxidation part of LT-SCR, but also in the RHC reaction cascade

An experimental and modelling study of the reactivity of adsorbed NH3 in the low temperature NH3-SCR reduction half-cycle over a Cu-CHA catalyst

The reactivity of Lewis and Brønsted ammonia in the reduction half-cycle (RHC) of the NH3-SCR low temperature redox mechanism was studied over a model Cu−CHA catalyst by transient kinetic tests involving reductive NO pulses. The CuII sites were reduced according to a 1:1:1:1 molar ratio with NO and NH3 conversion and N2 formation. The ammonia coordinated to Cu sites (Lewis ammonia) was preferentially consumed prior to that stored on the Brønsted acid sites. The catalyst was effectively re-oxidized by O2 in He at 150 °C even when the Cu-coordinated ammonia was depleted. A redox kinetic model assuming NO activation by CuII to a gaseous mobile intermediate (HONO) which reacts first with Lewis-NH3 and then with Brønsted-NH3 was successfully fitted to our transient data assuming the CuII reduction rate to be second order in the CuII sites. This suggests a possible role of CuII dimeric complexes in the RHC of Standard SCR