EMB-505 Captain reported the loss of cabin pressurization during cruise. The flight crew diverted to an appropriate airport.

Narrative

The flight departed from Runway XX at ZZZ1 in good VFR conditions. Following takeoff; we were assigned an eastbound heading by Departure Control. The aircraft climbed smoothly to FL430. During the climb; standard procedures were completed; including the cabin pressurization check and transition to standard pressure (29.92 inHg).At cruise; the aircraft was operating at Mach 0.75 and 430 KTAS. Due to a 45-kt. headwind; I opted to carry extra fuel; ensuring approximately 1500 lbs upon arrival at ZZZ2; which was within acceptable reserves for VFR operations.While at FL430; I began monitoring the Environmental Control System (ECS) synoptic page and noticed an abnormal temperature rise on the right-hand heat exchanger; with readings nearing 150°C--well above normal operating range.Shortly after accessing the ECS page; the CAS system displayed an ALERT: 'DUCT 2 OVERTEMP.' I immediately referenced the appropriate checklist and began executing procedures. Given the seriousness of the indication; I initiated a descent to FL360 to offload thermal stress and improve ECS cooling performance.However; during descent; as we passed FL410; a second CAS message illuminated: 'DUCT 1 OVERTEMP.' This indicated both ECS ducting systems were now overheating. At FL400; an additional alert was triggered: 'CABIN ALTITUDE HI;' signaling a loss of cabin pressurization.Actions Taken: Requested priority handling - Executed memory items for CABIN ALT HI (Don oxygen masks; establish crew communication; initiate descent).Requested priority handling with ATC and initiated a rapid emergency descent to 10;000 ft.Requested and received vectors to the nearest suitable airport: ZZZ.Maintained full control of the aircraft; monitored cabin and ECS parameters.Landed safely at ZZZ with no injuries or aircraft damage.Maintenance Findings:Following the flight; the aircraft was ferried to ZZZ2. After inspection; the following issues were identified:The RAM air valve was found fully shut; preventing proper airflow through the ECS during flight. This valve is designed to open in flight to allow ambient air for ECS cooling.Multiple ECS temperature sensors were found to be faulty; which likely triggered or contributed to the overtemperature alerts and misleading system indications.