Understanding the mechanochemical synthesis of manganite perovskites and their catalytic behaviour

The tightening of emission regulations and increasing prices of precious metals for existing commercial catalysts drives the need to develop of new sustainable catalysts at lower performance costs. Mechanochemistry offers a solventless, ‘one-step’ route to preparing metal oxide catalysts, however, there is limited information on the chemical steps involved. The use of multiple advanced characterisation techniques, such as HERFD, XES and NAP-XPS, has been applied in this work to understand the structure of the highly disordered and heterogeneous materials produced by ball milling. This thesis has provided further insights to begin to form generalised rules for the mechanochemical synthesis of mixed metal oxides, such as perovskites. In doing so, it can start to aid the rational design of new catalyst technologies. A predominant part of the work within this thesis has focused on the mechanochemical synthesis of LaMnO3. Preforming XAS on ex situ ‘time slices’ during the milling procedure was successful in providing insights into the underlying chemistry; not previously possible by lab-based XRD. The XAS data showed the La precursor to disperse readily over Mn2O3 at the early stages of milling. On increasing the milling time it allowed for mechanical activation of both precursors and the formation of powdered LaMnO3, with no calcination step required. Applying the same milling conditions as for LaMnO3 to the synthesis of other manganite perovskites, ErMnO3 and YMnO3, did not result in the desired phase, with a highly amorphous material produced. This highlights the intrinsic difficulties with regards to the mechanochemical syntheses; often each individual system requires specific optimisation to reach the desired material properties. However, exploring the effect of La dispersion at low mechanical energies was shown to be effective in another system, Au/Al2O3. Challenges regarding the in situ monitoring of mechanochemistry have been addressed within this work. Difficulties in the dynamic set-up of commercial milling equipment has meant in situ monitoring of planetary ball milling is not possible. However, the work here attempted a modified in situ mill and in situ high pressure experiments to mimic those experienced during mechanochemistry. It was able to show the challenges in (1) monitoring mixed metal oxide systems in real-time and (2) mimicking impact forces occurring as a result of mechanical action. Surface sensitive studies, such as XPS, have been crucial in determining improved catalytic activity towards deN2O for the ball milled LaMnO3. Following the reaction under working conditions via NAP-XPS, the increased activity at lower reaction temperatures was accredited, not to changes in the catalytic active site Mn, but to increased surface oxygen vacancies, and the presence -OH within the La 3d XPS region. This research demonstrates by collating a large variety of complementary characterisation techniques it has produced new insights into the mechanochemical synthesis of manganite perovskites. However, it also highlights the continued innovation and development required for the analysis of highly complex materials and equipment setups

Dataset for 'The electronic structure, surface properties, and in situ N2O decomposition of mechanochemically synthesised LaMnO3'

This dataset supports the publication: Rachel H. Blackmore, Maria Elena Rivas, George Tierney, Khaled M. H. Mohammed, Donato Decarolis, Shusaku Hayama, Federica Venturini, Georg Held, Rosa Arrigo, Monica Amboage, Pip Hellier, Evan Lynch, Mahrez Amri, Marianna Casavola, Tugce Eralp Erden, Paul Collier and Peter P. Wells. The electronic structure, surface properties, and in situ N2O decomposition of mechanochemically synthesised LaMnO3. Physical Chemistry Chemical Physics Journal (PCCP)</span

Dataset for &#39;Understanding the Mechanochemical Synthesis of Manganite Perovskites and their Catalytic Behaviour&#39;

This dataset supports University of Southampton PhD thesis &#39;Understanding the Mechanochemical Synthesis of Manganite Perovskites and their Catalytic Behaviour&#39;</span

Assessment, endoscopy, and treatment in patients with acute severe ulcerative colitis during the COVID-19 pandemic (PROTECT-ASUC): a multicentre, observational, case-control study

BackgroundThere is a paucity of evidence to support safe and effective management of patients with acute severe ulcerative colitis during the COVID-19 pandemic. We sought to identify alterations to established conventional evidence-based management of acute severe ulcerative colitis during the early COVID-19 pandemic, the effect on outcomes, and any associations with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and severe COVID-19 outcomes. MethodsThe PROTECT-ASUC study was a multicentre, observational, case-control study in 60 acute secondary care hospitals throughout the UK. We included adults (≥18 years) with either ulcerative colitis or inflammatory bowel disease unclassified, who presented with acute severe ulcerative colitis and fulfilled the Truelove and Witts criteria. Cases and controls were identified as either admitted or managed in emergency ambulatory care settings between March 1, 2020, and June 30, 2020 (COVID-19 pandemic period cohort), or between Jan 1, 2019, and June 30, 2019 (historical control cohort), respectively. The primary outcome was the proportion of patients with acute severe ulcerative colitis receiving rescue therapy (including primary induction) or colectomy. The study is registered with ClinicalTrials.gov, NCT04411784. FindingsWe included 782 patients (398 in the pandemic period cohort and 384 in the historical control cohort) who met the Truelove and Witts criteria for acute severe ulcerative colitis. The proportion of patients receiving rescue therapy (including primary induction) or surgery was higher during the pandemic period than in the historical period (217 [55%] of 393 patients vs 159 [42%] of 380 patients; p=0·00024) and the time to rescue therapy was shorter in the pandemic cohort than in the historical cohort (p=0·0026). This difference was driven by a greater use of rescue and primary induction therapies with biologicals, ciclosporin, or tofacitinib in the COVID-19 pandemic period cohort than in the historical control period cohort (177 [46%] of 387 patients in the COVID-19 cohort vs 134 [36%] of 373 patients in the historical cohort; p=0·0064). During the pandemic, more patients received ambulatory (outpatient) intravenous steroids (51 [13%] of 385 patients vs 19 [5%] of 360 patients; p=0·00023). Fewer patients received thiopurines (29 [7%] of 398 patients vs 46 [12%] of 384; p=0·029) and 5-aminosalicylic acids (67 [17%] of 398 patients vs 98 [26%] of 384; p=0·0037) during the pandemic than in the historical control period. Colectomy rates were similar between the pandemic and historical control groups (64 [16%] of 389 vs 50 [13%] of 375; p=0·26); however, laparoscopic surgery was less frequently performed during the pandemic period (34 [53%] of 64] vs 38 [76%] of 50; p=0·018). Five (2%) of 253 patients tested positive for SARS-CoV-2 during hospital treatment. Two (2%) of 103 patients re-tested for SARS-CoV-2 during the 3-month follow-up were positive 5 days and 12 days, respectively, after discharge from index admission. Both recovered without serious outcomes. InterpretationThe COVID-19 pandemic altered practice patterns of gastroenterologists and colorectal surgeons in the management of acute severe ulcerative colitis but was associated with similar outcomes to a historical cohort. Despite continued use of high-dose corticosteroids and biologicals, the incidence of COVID-19 within 3 months was low and not associated with adverse COVID-19 outcomes